diff --git a/include/core/capture/capture_base.h b/include/core/capture/capture_base.h
index 70fee2c15f074e571fd273d7cfccfbdc21c20552..2491d5a6a5afbdc4d3b52a3e86003c3794b6cd81 100644
--- a/include/core/capture/capture_base.h
+++ b/include/core/capture/capture_base.h
@@ -79,6 +79,8 @@ class CaptureBase : public NodeBase, public HasStateBlocks, public std::enable_s
     public:
         unsigned int getHits() const;
         const FactorBasePtrList& getConstrainedByList() const;
+        bool isConstrainedBy(const FactorBasePtr &_factor) const;
+
 
         // State blocks
         const std::string& getStructure() const;
@@ -183,6 +185,7 @@ inline const FactorBasePtrList& CaptureBase::getConstrainedByList() const
     return constrained_by_list_;
 }
 
+
 inline TimeStamp CaptureBase::getTimeStamp() const
 {
     return time_stamp_;
diff --git a/include/core/common/wolf.h b/include/core/common/wolf.h
index 9f548fd325de45d8901f432975bf23563938c988..64a4741c518ecd0f75bf029aa4e3267b1e3f8c4e 100644
--- a/include/core/common/wolf.h
+++ b/include/core/common/wolf.h
@@ -195,7 +195,11 @@ struct MatrixSizeCheck
         typedef std::list<ClassName##Ptr>             ClassName##PtrList; \
         typedef ClassName##PtrList::iterator          ClassName##Iter; \
         typedef ClassName##PtrList::const_iterator    ClassName##ConstIter; \
-        typedef ClassName##PtrList::reverse_iterator  ClassName##RevIter;
+        typedef ClassName##PtrList::reverse_iterator  ClassName##RevIter; \
+        typedef std::list<ClassName##WPtr>            ClassName##WPtrList; \
+        typedef ClassName##WPtrList::iterator         ClassName##WIter; \
+        typedef ClassName##WPtrList::const_iterator   ClassName##WConstIter; \
+        typedef ClassName##WPtrList::reverse_iterator ClassName##WRevIter;
 
 #define WOLF_STRUCT_PTR_TYPEDEFS(StructName) \
         struct StructName; \
diff --git a/include/core/factor/factor_base.h b/include/core/factor/factor_base.h
index 6f215396071b757b980faac31be8d0250716ea71..cd1439f96e437dc39dde137dd1014f37abee10db 100644
--- a/include/core/factor/factor_base.h
+++ b/include/core/factor/factor_base.h
@@ -40,19 +40,19 @@ class FactorBase : public NodeBase, public std::enable_shared_from_this<FactorBa
 {
   friend FeatureBase;
     private:
-        FeatureBaseWPtr feature_ptr_;                    ///< FeatureBase pointer (upper node)
+        FeatureBaseWPtr feature_ptr_;                       ///< FeatureBase pointer (upper node)
 
         static unsigned int factor_id_count_;
 
     protected:
         unsigned int factor_id_;
-        FactorStatus status_;                           ///< status of factor
-        bool apply_loss_function_;                      ///< flag for applying loss function to this factor
-        FrameBaseWPtr frame_other_ptr_;                 ///< FrameBase pointer
-        CaptureBaseWPtr capture_other_ptr_;             ///< CaptureBase pointer
-        FeatureBaseWPtr feature_other_ptr_;             ///< FeatureBase pointer
-        LandmarkBaseWPtr landmark_other_ptr_;           ///< LandmarkBase pointer
-        ProcessorBaseWPtr processor_ptr_;               ///< ProcessorBase pointer
+        FactorStatus status_;                               ///< status of factor
+        bool apply_loss_function_;                          ///< flag for applying loss function to this factor
+        FrameBaseWPtrList frame_other_list_;                ///< FrameBase pointer list
+        CaptureBaseWPtrList capture_other_list_;            ///< CaptureBase pointer list
+        FeatureBaseWPtrList feature_other_list_;            ///< FeatureBase pointer list
+        LandmarkBaseWPtrList landmark_other_list_;          ///< LandmarkBase pointer list
+        ProcessorBaseWPtr processor_ptr_;                   ///< ProcessorBase pointer list
 
         virtual void setProblem(ProblemPtr) final;
     public:
@@ -72,6 +72,17 @@ class FactorBase : public NodeBase, public std::enable_shared_from_this<FactorBa
                    bool _apply_loss_function,
                    FactorStatus _status = FAC_ACTIVE);
 
+        FactorBase(const std::string&  _tp,
+                   const FrameBasePtrList& _frame_other_list,
+                   const CaptureBasePtrList& _capture_other_list,
+                   const FeatureBasePtrList& _feature_other_list,
+                   const LandmarkBasePtrList& _landmark_other_list,
+                   const ProcessorBasePtr& _processor_ptr,
+                   bool _apply_loss_function,
+                   FactorStatus _status = FAC_ACTIVE);
+
+
+
         virtual ~FactorBase() = default;
 
         virtual void remove(bool viral_remove_empty_parent=false);
@@ -133,6 +144,14 @@ class FactorBase : public NodeBase, public std::enable_shared_from_this<FactorBa
          **/
         CaptureBasePtr getCapture() const;
 
+        /** \brief Returns a pointer to its frame
+         **/
+        FrameBasePtr getFrame() const;
+
+        /** \brief Returns a pointer to its capture's sensor
+         **/
+        SensorBasePtr getSensor() const;
+
         /** \brief Returns the factor residual size
          **/
         virtual unsigned int getSize() const = 0;
@@ -149,21 +168,32 @@ class FactorBase : public NodeBase, public std::enable_shared_from_this<FactorBa
          */
         bool getApplyLossFunction() const;
 
-        /** \brief Returns a pointer to the frame constrained to
+        /** \brief Returns a pointer to the first frame constrained to
          **/
-        FrameBasePtr getFrameOther() const       { return frame_other_ptr_.lock(); }
+        FrameBasePtr getFrameOther() const;
 
-        /** \brief Returns a pointer to the capture constrained to
+        /** \brief Returns a pointer to the first capture constrained to
          **/
-        CaptureBasePtr getCaptureOther() const       { return capture_other_ptr_.lock(); }
+        CaptureBasePtr getCaptureOther() const;
 
-        /** \brief Returns a pointer to the feature constrained to
+        /** \brief Returns a pointer to the first feature constrained to
          **/
-        FeatureBasePtr getFeatureOther() const       { return feature_other_ptr_.lock(); }
+        FeatureBasePtr getFeatureOther() const;
 
-        /** \brief Returns a pointer to the landmark constrained to
+        /** \brief Returns a pointer to the first landmark constrained to
          **/
-        LandmarkBasePtr getLandmarkOther() const     { return landmark_other_ptr_.lock(); }
+        LandmarkBasePtr getLandmarkOther() const;
+
+        // get pointer lists to other nodes
+        FrameBaseWPtrList getFrameOtherList() const         { return frame_other_list_; }
+        CaptureBaseWPtrList getCaptureOtherList() const     { return capture_other_list_; }
+        FeatureBaseWPtrList getFeatureOtherList() const     { return feature_other_list_; }
+        LandmarkBaseWPtrList getLandmarkOtherList() const   { return landmark_other_list_; }
+
+        bool hasFrameOther(const FrameBasePtr& _frm_other) const;
+        bool hasCaptureOther(const CaptureBasePtr& _cap_other) const;
+        bool hasFeatureOther(const FeatureBasePtr& _ftr_other) const;
+        bool hasLandmarkOther(const LandmarkBasePtr& _lmk_other) const;
 
     public:
         /**
@@ -228,6 +258,39 @@ inline bool FactorBase::getApplyLossFunction() const
     return apply_loss_function_;
 }
 
+inline FrameBasePtr FactorBase::getFrameOther() const
+{
+    if (frame_other_list_.empty()) return nullptr;
+    if (frame_other_list_.front().expired()) return nullptr;
+
+    return frame_other_list_.front().lock();
+}
+
+inline CaptureBasePtr FactorBase::getCaptureOther() const
+{
+    if (capture_other_list_.empty()) return nullptr;
+    if (capture_other_list_.front().expired()) return nullptr;
+
+    return capture_other_list_.front().lock();
+}
+
+inline FeatureBasePtr FactorBase::getFeatureOther() const
+{
+    if (feature_other_list_.empty()) return nullptr;
+    if (feature_other_list_.front().expired()) return nullptr;
+
+    return feature_other_list_.front().lock();
+}
+
+inline LandmarkBasePtr FactorBase::getLandmarkOther() const
+{
+    if (landmark_other_list_.empty()) return nullptr;
+    if (landmark_other_list_.front().expired()) return nullptr;
+
+    return landmark_other_list_.front().lock();
+}
+
+
 inline ProcessorBasePtr FactorBase::getProcessor() const
 {
   return processor_ptr_.lock();
diff --git a/include/core/factor/factor_diff_drive.h b/include/core/factor/factor_diff_drive.h
index 2338f699de73d38c74ce13509cdc0b70a1a82130..d936a99d6c1d64f29fda2c5aeca1806e0065c4d1 100644
--- a/include/core/factor/factor_diff_drive.h
+++ b/include/core/factor/factor_diff_drive.h
@@ -140,10 +140,12 @@ inline bool FactorDiffDrive::operator ()(const T* const _p1, const T* const _o1,
 inline Eigen::VectorXd FactorDiffDrive::residual()
 {
     VectorXd residual(3);
-    operator ()(getFrameOther()->getP()->getState().data(), getFrameOther()->getO()->getState().data(),
-                getCapture()->getFrame()->getP()->getState().data(),
-                getCapture()->getFrame()->getO()->getState().data(),
-                getCaptureOther()->getSensorIntrinsic()->getState().data(), residual.data());
+    operator ()(getFrameOther()   ->getP()               ->getState() .data(),
+                getFrameOther()   ->getO()               ->getState() .data(),
+                getFrame()        ->getP()               ->getState() .data(),
+                getFrame()        ->getO()               ->getState() .data(),
+                getCaptureOther() ->getSensorIntrinsic() ->getState() .data(),
+                residual.data());
     return residual;
 }
 
diff --git a/include/core/feature/feature_base.h b/include/core/feature/feature_base.h
index 7203425913de8bb5a3ff5a0fb267b4aef98f9fd5..a2ba3bc60f5d0db16d6c486099ac5e3e9b3116ec 100644
--- a/include/core/feature/feature_base.h
+++ b/include/core/feature/feature_base.h
@@ -95,6 +95,9 @@ class FeatureBase : public NodeBase, public std::enable_shared_from_this<Feature
 
         unsigned int getHits() const;
         const FactorBasePtrList& getConstrainedByList() const;
+        bool isConstrainedBy(const FactorBasePtr &_factor) const;
+
+
 
         // all factors
         void getFactorList(FactorBasePtrList & _fac_list) const;
diff --git a/include/core/frame/frame_base.h b/include/core/frame/frame_base.h
index 3745de04806c78f65463c39da49bcf9ba42cf0f8..eea8873b3e804743f4cd224bffd6442d4c17febf 100644
--- a/include/core/frame/frame_base.h
+++ b/include/core/frame/frame_base.h
@@ -126,6 +126,7 @@ class FrameBase : public NodeBase, public HasStateBlocks, public std::enable_sha
         void getFactorList(FactorBasePtrList& _fac_list) const;
         unsigned int getHits() const;
         const FactorBasePtrList& getConstrainedByList() const;
+        bool isConstrainedBy(const FactorBasePtr& _factor) const;
         void link(TrajectoryBasePtr);
         template<typename classType, typename... T>
         static std::shared_ptr<classType> emplace(TrajectoryBasePtr _ptr, T&&... all);
diff --git a/include/core/landmark/landmark_base.h b/include/core/landmark/landmark_base.h
index 2f80a3d6fbe26d171126a82d280e65a3acaf4349..254e03e480f8471029c38c8f59626b230dc962f9 100644
--- a/include/core/landmark/landmark_base.h
+++ b/include/core/landmark/landmark_base.h
@@ -71,6 +71,8 @@ class LandmarkBase : public NodeBase, public HasStateBlocks, public std::enable_
 
         unsigned int getHits() const;
         const FactorBasePtrList& getConstrainedByList() const;
+        bool isConstrainedBy(const FactorBasePtr &_factor) const;
+
 
         MapBasePtr getMap() const;
         void link(MapBasePtr);
diff --git a/include/core/state_block/has_state_blocks.h b/include/core/state_block/has_state_blocks.h
index 97c570cb8550d5fb9aa6a2bf076e7e9674ab75c5..07c6d757bc09125c4a4e8a55aefd6d37b480c7d4 100644
--- a/include/core/state_block/has_state_blocks.h
+++ b/include/core/state_block/has_state_blocks.h
@@ -48,10 +48,13 @@ class HasStateBlocks
         virtual unsigned int    removeStateBlock(const char _sb_type);
         bool            hasStateBlock(const std::string& _sb_type) const { return state_block_map_.count(_sb_type) > 0; }
         bool            hasStateBlock(const char _sb_type) const { return hasStateBlock(std::string(1, _sb_type)); }
+        bool            hasStateBlock(const StateBlockPtr& _sb) const;
         StateBlockPtr   getStateBlock(const std::string& _sb_type) const;
         StateBlockPtr   getStateBlock(const char _sb_type) const { return getStateBlock(std::string(1,_sb_type)); }
         bool            setStateBlock(const std::string _sb_type, const StateBlockPtr& _sb);
         bool            setStateBlock(const char _sb_type, const StateBlockPtr& _sb) { return setStateBlock(std::string(1, _sb_type), _sb); }
+        bool            stateBlockKey(const StateBlockPtr& _sb, std::string& _key) const;
+        std::unordered_map<std::string, StateBlockPtr>::const_iterator find(const StateBlockPtr& _sb) const;
 
         // Emplace derived state blocks (angle, quaternion, etc).
         template<typename SB, typename ... Args>
@@ -283,7 +286,49 @@ inline unsigned int HasStateBlocks::getSize(std::string _sub_structure) const
     return size;
 }
 
+//<<<<<<< HEAD
+inline std::unordered_map<std::string, StateBlockPtr>::const_iterator HasStateBlocks::find(const StateBlockPtr& _sb) const
+{
+    const auto& it = std::find_if(state_block_map_.begin(),
+                                  state_block_map_.end(),
+                                  [_sb](const std::pair<std::string, StateBlockPtr>& pair)
+                                  {
+                                    return pair.second == _sb;
+                                  }
+                                  );
+
+    return it;
+}
+
+inline bool HasStateBlocks::hasStateBlock(const StateBlockPtr &_sb) const
+{
+    const auto& it = this->find(_sb);
+
+    return it != state_block_map_.end();
+}
+
+inline bool HasStateBlocks::stateBlockKey(const StateBlockPtr &_sb, std::string& _key) const
+{
+    const auto& it = this->find(_sb);
+
+    bool found = (it != state_block_map_.end());
+
+    if (found)
+    {
+        _key = it->first;
+        return true;
+    }
+    else
+    {
+        _key = "";
+        return false;
+    }
+}
+
+//inline unsigned int HasStateBlocks::getLocalSize() const
+//=======
 inline unsigned int HasStateBlocks::getLocalSize(std::string _sub_structure) const
+//>>>>>>> devel
 {
     if (_sub_structure == ""){
         _sub_structure = structure_;
@@ -302,4 +347,5 @@ inline unsigned int HasStateBlocks::getLocalSize(std::string _sub_structure) con
 }
 
 } // namespace wolf
+
 #endif /* STATE_BLOCK_HAS_STATE_BLOCKS_H_ */
diff --git a/include/core/utils/check_log.hpp b/include/core/utils/check_log.hpp
index db3ab2dc9dd6e165c3541544bf7770022568f2fe..844b4d8ea60821ae18b6a9912d343de703163814 100644
--- a/include/core/utils/check_log.hpp
+++ b/include/core/utils/check_log.hpp
@@ -2,31 +2,42 @@
 #define CHECK_LOG_HPP
 #include <iostream>
 #include <string>
+#include <sstream>
 
-class CheckLog {
+namespace wolf
+{
+class CheckLog
+{
+  public:
+    bool        is_consistent_;
+    std::string explanation_;
 
-public:
-
-  bool is_consistent_;
-  std::string explanation_;
-
-  CheckLog() {
-    is_consistent_ = true;
-    explanation_ = "";
-  }
-  CheckLog(bool consistent, std::string explanation) {
-    is_consistent_ = consistent;
-    if (not consistent)
-      explanation_ = explanation;
-    else
-      explanation_ = "";
-  }
-  ~CheckLog(){};
-  void compose(CheckLog l) {
-
-    CheckLog result_log;
-    is_consistent_ = is_consistent_ and l.is_consistent_;
-    explanation_ = explanation_ + l.explanation_;
-  }
+    CheckLog()
+    {
+        is_consistent_ = true;
+        explanation_   = "";
+    }
+    CheckLog(bool _consistent, std::string _explanation)
+    {
+        is_consistent_ = _consistent;
+        if (not _consistent)
+            explanation_ = _explanation;
+        else
+            explanation_ = "";
+    }
+    ~CheckLog(){};
+    void compose(CheckLog l)
+    {
+        is_consistent_ = is_consistent_ and l.is_consistent_;
+        explanation_   = explanation_ + l.explanation_;
+    }
+    void assertTrue(bool _condition, std::stringstream& _stream)
+    {
+        auto cl = CheckLog(_condition, _stream.str());
+        this->compose(cl);
+        // Clear inconsistency_explanation
+        std::stringstream().swap(_stream);
+    }
 };
+}  // namespace wolf
 #endif
diff --git a/src/capture/capture_base.cpp b/src/capture/capture_base.cpp
index 54e5d2a3cdedb301a7580e691cad9543df3c24c2..d07b9b055d8197593dbdde99d05f6a4eddd46bfe 100644
--- a/src/capture/capture_base.cpp
+++ b/src/capture/capture_base.cpp
@@ -130,6 +130,22 @@ void CaptureBase::removeConstrainedBy(FactorBasePtr _fac_ptr)
     constrained_by_list_.remove(_fac_ptr);
 }
 
+bool CaptureBase::isConstrainedBy(const FactorBasePtr &_factor) const
+{
+    FactorBaseConstIter cby_it = std::find_if(constrained_by_list_.begin(),
+                                              constrained_by_list_.end(),
+                                              [_factor](const FactorBasePtr & cby)
+                                              {
+                                                 return cby == _factor;
+                                              }
+                                              );
+    if (cby_it != constrained_by_list_.end())
+        return true;
+    else
+        return false;
+}
+
+
 const std::string& CaptureBase::getStructure() const
 {
     if (getSensor())
diff --git a/src/factor/factor_base.cpp b/src/factor/factor_base.cpp
index 46b244d9e83f9c01f4fca0bf84af35d81d36d53f..72b36c519a0d8d0ce2cb7ac4748e0dfc110026d0 100644
--- a/src/factor/factor_base.cpp
+++ b/src/factor/factor_base.cpp
@@ -19,15 +19,52 @@ FactorBase::FactorBase(const std::string&  _tp,
     factor_id_(++factor_id_count_),
     status_(_status),
     apply_loss_function_(_apply_loss_function),
-    frame_other_ptr_(_frame_other_ptr),
-    capture_other_ptr_(_capture_other_ptr),
-    feature_other_ptr_(_feature_other_ptr),
-    landmark_other_ptr_(_landmark_other_ptr),
+    frame_other_list_(),
+    capture_other_list_(),
+    feature_other_list_(),
+    landmark_other_list_(),
     processor_ptr_(_processor_ptr)
 {
-//    std::cout << "constructed        +c" << id() << std::endl;
+    if (_frame_other_ptr)
+        frame_other_list_.push_back(_frame_other_ptr);
+    if (_capture_other_ptr)
+        capture_other_list_.push_back(_capture_other_ptr);
+    if (_feature_other_ptr)
+        feature_other_list_.push_back(_feature_other_ptr);
+    if (_landmark_other_ptr)
+        landmark_other_list_.push_back(_landmark_other_ptr);
 }
 
+FactorBase::FactorBase(const std::string&  _tp,
+                       const FrameBasePtrList& _frame_other_list,
+                       const CaptureBasePtrList& _capture_other_list,
+                       const FeatureBasePtrList& _feature_other_list,
+                       const LandmarkBasePtrList& _landmark_other_list,
+                       const ProcessorBasePtr& _processor_ptr,
+                       bool _apply_loss_function,
+                       FactorStatus _status) :
+            NodeBase("FACTOR", _tp),
+            feature_ptr_(),
+            factor_id_(++factor_id_count_),
+            status_(_status),
+            apply_loss_function_(_apply_loss_function),
+            frame_other_list_(),
+            capture_other_list_(),
+            feature_other_list_(),
+            landmark_other_list_(),
+            processor_ptr_(_processor_ptr)
+{
+    for (auto& Fo : _frame_other_list)
+        frame_other_list_.push_back(Fo);
+    for (auto& Co : _capture_other_list)
+        capture_other_list_.push_back(Co);
+    for (auto& fo : _feature_other_list)
+        feature_other_list_.push_back(fo);
+    for (auto& Lo : landmark_other_list_)
+        landmark_other_list_.push_back(Lo);
+}
+
+
 void FactorBase::remove(bool viral_remove_empty_parent)
 {
     if (!is_removing_)
@@ -46,36 +83,48 @@ void FactorBase::remove(bool viral_remove_empty_parent)
             getProblem()->notifyFactor(this_fac,REMOVE);
 
         // remove other: {Frame, Capture, Feature, Landmark}
-        FrameBasePtr frm_o = frame_other_ptr_.lock();
-        if (frm_o)
+        for (auto& frm_ow : frame_other_list_)
         {
-            frm_o->removeConstrainedBy(this_fac);
-            if (frm_o->getConstrainedByList().empty() && frm_o->getCaptureList().empty())
-                frm_o->remove(viral_remove_empty_parent);
+            auto frm_o = frm_ow.lock();
+            if (frm_o)
+            {
+                frm_o->removeConstrainedBy(this_fac);
+                if (frm_o->getConstrainedByList().empty() && frm_o->getCaptureList().empty())
+                    frm_o->remove(viral_remove_empty_parent);
+            }
         }
 
-        CaptureBasePtr cap_o = capture_other_ptr_.lock();
-        if (cap_o)
+        for (auto& cap_ow : capture_other_list_)
         {
-            cap_o->removeConstrainedBy(this_fac);
-            if (cap_o->getConstrainedByList().empty() && cap_o->getFeatureList().empty())
-                cap_o->remove(viral_remove_empty_parent);
+            auto cap_o = cap_ow.lock();
+            if (cap_o)
+            {
+                cap_o->removeConstrainedBy(this_fac);
+                if (cap_o->getConstrainedByList().empty() && cap_o->getFeatureList().empty())
+                    cap_o->remove(viral_remove_empty_parent);
+            }
         }
 
-        FeatureBasePtr ftr_o = feature_other_ptr_.lock();
-        if (ftr_o)
+        for (auto& ftr_ow : feature_other_list_)
         {
-            ftr_o->removeConstrainedBy(this_fac);
-            if (ftr_o->getConstrainedByList().empty() && ftr_o->getFactorList().empty())
-                ftr_o->remove(viral_remove_empty_parent);
+            auto ftr_o = ftr_ow.lock();
+            if (ftr_o)
+            {
+                ftr_o->removeConstrainedBy(this_fac);
+                if (ftr_o->getConstrainedByList().empty() && ftr_o->getFactorList().empty())
+                    ftr_o->remove(viral_remove_empty_parent);
+            }
         }
 
-        LandmarkBasePtr lmk_o = landmark_other_ptr_.lock();
-        if (lmk_o)
+        for (auto& lmk_ow : landmark_other_list_)
         {
-            lmk_o->removeConstrainedBy(this_fac);
-            if (lmk_o->getConstrainedByList().empty())
-                lmk_o->remove(viral_remove_empty_parent);
+            auto lmk_o = lmk_ow.lock();
+            if (lmk_o)
+            {
+                lmk_o->removeConstrainedBy(this_fac);
+                if (lmk_o->getConstrainedByList().empty())
+                    lmk_o->remove(viral_remove_empty_parent);
+            }
         }
 
         //        std::cout << "Removed             c" << id() << std::endl;
@@ -106,6 +155,18 @@ CaptureBasePtr FactorBase::getCapture() const
     return getFeature()->getCapture();
 }
 
+FrameBasePtr FactorBase::getFrame() const
+{
+    assert(getCapture() != nullptr && "calling getFrame before linking with a capture");
+    return getCapture()->getFrame();
+}
+
+SensorBasePtr FactorBase::getSensor() const
+{
+    assert(getCapture() != nullptr && "calling getSensor before linking with a capture");
+    return getCapture()->getSensor();
+}
+
 void FactorBase::setStatus(FactorStatus _status)
 {
     if (getProblem() == nullptr)
@@ -120,6 +181,66 @@ void FactorBase::setStatus(FactorStatus _status)
     status_ = _status;
 }
 
+bool FactorBase::hasFrameOther(const FrameBasePtr &_frm_other) const
+{
+    FrameBaseWConstIter frm_it = find_if(frame_other_list_.begin(),
+                                         frame_other_list_.end(),
+                                         [_frm_other](const FrameBaseWPtr &frm_ow)
+                                         {
+                                             return frm_ow.lock() == _frm_other;
+                                         }
+    );
+    if (frm_it != frame_other_list_.end())
+        return true;
+
+    return false;
+}
+
+bool FactorBase::hasCaptureOther(const CaptureBasePtr &_cap_other) const
+{
+    CaptureBaseWConstIter cap_it = find_if(capture_other_list_.begin(),
+                                           capture_other_list_.end(),
+                                           [_cap_other](const CaptureBaseWPtr &cap_ow)
+                                           {
+                                               return cap_ow.lock() == _cap_other;
+                                           }
+    );
+    if (cap_it != capture_other_list_.end())
+        return true;
+
+    return false;
+}
+
+bool FactorBase::hasFeatureOther(const FeatureBasePtr &_ftr_other) const
+{
+    FeatureBaseWConstIter ftr_it = find_if(feature_other_list_.begin(),
+                                           feature_other_list_.end(),
+                                           [_ftr_other](const FeatureBaseWPtr &ftr_ow)
+                                           {
+                                               return ftr_ow.lock() == _ftr_other;
+                                           }
+    );
+    if (ftr_it != feature_other_list_.end())
+        return true;
+
+    return false;
+}
+
+bool FactorBase::hasLandmarkOther(const LandmarkBasePtr &_lmk_other) const
+{
+    LandmarkBaseWConstIter lmk_it = find_if(landmark_other_list_.begin(),
+                                            landmark_other_list_.end(),
+                                            [_lmk_other](const LandmarkBaseWPtr &lmk_ow)
+                                            {
+                                                return lmk_ow.lock() == _lmk_other;
+                                            }
+                                            );
+    if (lmk_it != landmark_other_list_.end())
+        return true;
+
+    return false;
+}
+
 //void FactorBase::setApplyLossFunction(const bool _apply)
 //{
 //    apply_loss_function_ = _apply;
@@ -146,14 +267,26 @@ void FactorBase::link(FeatureBasePtr _ftr_ptr)
     this->setProblem(_ftr_ptr->getProblem());
 
     // constrained by
-    auto frame_other = this->frame_other_ptr_.lock();
-    if(frame_other != nullptr) frame_other->addConstrainedBy(shared_from_this());
-    auto capture_other = this->capture_other_ptr_.lock();
-    if(capture_other != nullptr) capture_other->addConstrainedBy(shared_from_this());
-    auto feature_other = this->feature_other_ptr_.lock();
-    if(feature_other != nullptr) feature_other->addConstrainedBy(shared_from_this());
-    auto landmark_other = this->landmark_other_ptr_.lock();
-    if(landmark_other != nullptr) landmark_other->addConstrainedBy(shared_from_this());
+    for (auto& frm_ow : frame_other_list_)
+    {
+        auto frame_other = frm_ow.lock();
+        if(frame_other != nullptr) frame_other->addConstrainedBy(shared_from_this());
+    }
+    for (auto& cap_ow : capture_other_list_)
+    {
+        auto capture_other = cap_ow.lock();
+        if(capture_other != nullptr) capture_other->addConstrainedBy(shared_from_this());
+    }
+    for (auto& ftr_ow : feature_other_list_)
+    {
+        auto feature_other = ftr_ow.lock();
+        if(feature_other != nullptr) feature_other->addConstrainedBy(shared_from_this());
+    }
+    for (auto& lmk_ow : landmark_other_list_)
+    {
+        auto landmark_other = lmk_ow.lock();
+        if(landmark_other != nullptr) landmark_other->addConstrainedBy(shared_from_this());
+    }
 }
 
 void FactorBase::setProblem(ProblemPtr _problem)
diff --git a/src/feature/feature_base.cpp b/src/feature/feature_base.cpp
index df5d1f1e7aa0f214adab2e0f74dc496623e7cf48..8dc3801efa5f93e5bd0df593442e4860cb75135e 100644
--- a/src/feature/feature_base.cpp
+++ b/src/feature/feature_base.cpp
@@ -92,6 +92,21 @@ void FeatureBase::removeConstrainedBy(FactorBasePtr _fac_ptr)
     constrained_by_list_.remove(_fac_ptr);
 }
 
+bool FeatureBase::isConstrainedBy(const FactorBasePtr &_factor) const
+{
+    FactorBaseConstIter cby_it = std::find_if(constrained_by_list_.begin(),
+                                              constrained_by_list_.end(),
+                                              [_factor](const FactorBasePtr & cby)
+                                              {
+                                                 return cby == _factor;
+                                              }
+                                              );
+    if (cby_it != constrained_by_list_.end())
+        return true;
+    else
+        return false;
+}
+
 const FactorBasePtrList& FeatureBase::getFactorList() const
 {
     return factor_list_;
diff --git a/src/frame/frame_base.cpp b/src/frame/frame_base.cpp
index 42a11b3782a5a669264471bcae49571ec1322840..c0f4d310e1062c9a68ea94a0ee0b70f912cd9d15 100644
--- a/src/frame/frame_base.cpp
+++ b/src/frame/frame_base.cpp
@@ -314,6 +314,21 @@ void FrameBase::removeConstrainedBy(FactorBasePtr _fac_ptr)
     constrained_by_list_.remove(_fac_ptr);
 }
 
+bool FrameBase::isConstrainedBy(const FactorBasePtr &_factor) const
+{
+    FactorBaseConstIter cby_it = std::find_if(constrained_by_list_.begin(),
+                                              constrained_by_list_.end(),
+                                              [_factor](const FactorBasePtr & cby)
+                                              {
+                                                 return cby == _factor;
+                                              }
+    );
+    if (cby_it != constrained_by_list_.end())
+        return true;
+    else
+        return false;
+}
+
 void FrameBase::link(TrajectoryBasePtr _trj_ptr)
 {
     assert(!is_removing_ && "linking a removed frame");
diff --git a/src/landmark/landmark_base.cpp b/src/landmark/landmark_base.cpp
index 7c9b8b664573bd296902ad420c1e5a161605e635..bc57f27294e6a0b05d67cbcf44725dd2b819f63b 100644
--- a/src/landmark/landmark_base.cpp
+++ b/src/landmark/landmark_base.cpp
@@ -138,6 +138,21 @@ void LandmarkBase::removeConstrainedBy(FactorBasePtr _fac_ptr)
     constrained_by_list_.remove(_fac_ptr);
 }
 
+bool LandmarkBase::isConstrainedBy(const FactorBasePtr &_factor) const
+{
+    FactorBaseConstIter cby_it = std::find_if(constrained_by_list_.begin(),
+                                              constrained_by_list_.end(),
+                                              [_factor](const FactorBasePtr & cby)
+                                              {
+                                                 return cby == _factor;
+                                              }
+                                              );
+    if (cby_it != constrained_by_list_.end())
+        return true;
+    else
+        return false;
+}
+
 LandmarkBasePtr LandmarkBase::create(const YAML::Node& _node)
 {
     unsigned int    id          = _node["id"]               .as< unsigned int     >();
diff --git a/src/problem/problem.cpp b/src/problem/problem.cpp
index e79de9572f545e85142450497f3d4780621adc7b..1d72f5b8fff0b187d192e575eb140a2e442f101e 100644
--- a/src/problem/problem.cpp
+++ b/src/problem/problem.cpp
@@ -925,227 +925,226 @@ void Problem::saveMap(const std::string& _filename_dot_yaml, const std::string&
     getMap()->save(_filename_dot_yaml, _map_name);
 }
 
-void Problem::print(int depth, std::ostream& stream, bool constr_by, bool metric, bool state_blocks) const
+void Problem::print(int _depth, std::ostream& _stream, bool _constr_by, bool _metric, bool _state_blocks) const
 {
 
-    stream << std::endl;
-    stream << "P: wolf tree status ---------------------" << std::endl;
-    stream << "Hardware" << ((depth < 1) ? ("   -- " + std::to_string(getHardware()->getSensorList().size()) + "S") : "")  << std::endl;
-    if (depth >= 1)
+    _stream << std::endl;
+    _stream << "P: wolf tree status ---------------------" << std::endl;
+    _stream << "Hardware" << ((_depth < 1) ? ("   -- " + std::to_string(getHardware()->getSensorList().size()) + "S") : "")  << std::endl;
+    if (_depth >= 1)
     {
         // Sensors =======================================================================================
         for (auto S : getHardware()->getSensorList())
         {
-            stream << "  Sen" << S->id() << " " << S->getType() << " \"" << S->getName() << "\"";
-            if (depth < 2)
-                stream << " -- " << S->getProcessorList().size() << "p";
-            stream << std::endl;
-            if (metric && state_blocks)
+            _stream << "  Sen" << S->id() << " " << S->getType() << " \"" << S->getName() << "\"";
+            if (_depth < 2)
+                _stream << " -- " << S->getProcessorList().size() << "p";
+            _stream << std::endl;
+            if (_metric && _state_blocks)
             {
-                stream << "    sb: ";
+                _stream << "    sb: ";
                 for (auto& _key : S->getStructure())
                 {
                     auto key = std::string(1,_key);
                     auto sb = S->getStateBlock(key);
-                    stream << key << "[" << (S->isStateBlockDynamic(key) ? "Dyn" : "Sta") << "," << (sb->isFixed() ? "Fix" : "Est") << "] = ( " << sb->getState().transpose() << " ); ";
+                    _stream << key << "[" << (S->isStateBlockDynamic(key) ? "Dyn" : "Sta") << "," << (sb->isFixed() ? "Fix" : "Est") << "] = ( " << sb->getState().transpose() << " ); ";
                 }
-                stream << std::endl;
+                _stream << std::endl;
             }
-            else if (metric)
+            else if (_metric)
             {
-                stream << "    ( ";
+                _stream << "    ( ";
                 for (auto& _key : S->getStructure())
                 {
                     auto key = std::string(1,_key);
                     auto sb = S->getStateBlock(key);
-                    stream << sb->getState().transpose() << " ";
+                    _stream << sb->getState().transpose() << " ";
                 }
-                stream << ")" << std::endl;
+                _stream << ")" << std::endl;
             }
-            else if (state_blocks)
+            else if (_state_blocks)
             {
-                stream << "    sb: ";
+                _stream << "    sb: ";
                 for (auto& _key : S->getStructure())
                 {
                     auto key = std::string(1,_key);
                     auto sb = S->getStateBlock(key);
-                    stream << key << "[" << (S->isStateBlockDynamic(key) ? "Dyn" : "Sta") << "," << (sb->isFixed() ? "Fix" : "Est") << "]; ";
+                    _stream << key << "[" << (S->isStateBlockDynamic(key) ? "Dyn" : "Sta") << "," << (sb->isFixed() ? "Fix" : "Est") << "]; ";
                 }
-                stream << std::endl;
+                _stream << std::endl;
             }
-            if (depth >= 2)
+            if (_depth >= 2)
             {
                 // Processors =======================================================================================
                 for (auto p : S->getProcessorList())
                 {
                     if (p->isMotion())
                     {
-                        stream << "    PrcM" << p->id() << " " << p->getType() << " \"" << p->getName() << "\"" << std::endl;
+                        _stream << "    PrcM" << p->id() << " " << p->getType() << " \"" << p->getName() << "\"" << std::endl;
                         ProcessorMotionPtr pm = std::static_pointer_cast<ProcessorMotion>(p);
                         if (pm->getOrigin())
-                            stream << "      o: C" << pm->getOrigin()->id() << " - " << (pm->getOrigin()->getFrame()->isKeyOrAux() ? (pm->getOrigin()->getFrame()->isKey() ? "  KFrm" : "  AFrm" ) : "  Frm")
+                            _stream << "      o: Cap" << pm->getOrigin()->id() << " - " << (pm->getOrigin()->getFrame()->isKeyOrAux() ? (pm->getOrigin()->getFrame()->isKey() ? "  KFrm" : "  AFrm" ) : "  Frm")
                             << pm->getOrigin()->getFrame()->id() << std::endl;
                         if (pm->getLast())
-                            stream << "      l: C" << pm->getLast()->id() << " - " << (pm->getLast()->getFrame()->isKeyOrAux() ? (pm->getLast()->getFrame()->isKey() ? "  KFrm" : " AFrm") : "  Frm")
+                            _stream << "      l: Cap" << pm->getLast()->id() << " - " << (pm->getLast()->getFrame()->isKeyOrAux() ? (pm->getLast()->getFrame()->isKey() ? "  KFrm" : " AFrm") : "  Frm")
                             << pm->getLast()->getFrame()->id() << std::endl;
                         if (pm->getIncoming())
-                            stream << "      i: C" << pm->getIncoming()->id() << std::endl;
+                            _stream << "      i: Cap" << pm->getIncoming()->id() << std::endl;
                     }
                     else
                     {
-                        stream << "    PrcT" << p->id() << " " << p->getType() << " \"" << p->getName() << "\"" << std::endl;
+                        _stream << "    PrcT" << p->id() << " " << p->getType() << " \"" << p->getName() << "\"" << std::endl;
                         ProcessorTrackerPtr pt = std::dynamic_pointer_cast<ProcessorTracker>(p);
                         if (pt)
                         {
                             if (pt->getOrigin())
-                                stream << "      o: C" << pt->getOrigin()->id() << " - " << (pt->getOrigin()->getFrame()->isKeyOrAux() ? (pt->getOrigin()->getFrame()->isKey() ? "  KFrm" : " AFrm") : "  Frm")
+                                _stream << "      o: Cap" << pt->getOrigin()->id() << " - " << (pt->getOrigin()->getFrame()->isKeyOrAux() ? (pt->getOrigin()->getFrame()->isKey() ? "  KFrm" : " AFrm") : "  Frm")
                                 << pt->getOrigin()->getFrame()->id() << std::endl;
                             if (pt->getLast())
-                                stream << "      l: C" << pt->getLast()->id() << " - " << (pt->getLast()->getFrame()->isKeyOrAux() ? (pt->getLast()->getFrame()->isKey() ? "  KFrm" : " AFrm") : "  Frm")
+                                _stream << "      l: Cap" << pt->getLast()->id() << " - " << (pt->getLast()->getFrame()->isKeyOrAux() ? (pt->getLast()->getFrame()->isKey() ? "  KFrm" : " AFrm") : "  Frm")
                                 << pt->getLast()->getFrame()->id() << std::endl;
                             if (pt->getIncoming())
-                                stream << "      i: C" << pt->getIncoming()->id() << std::endl;
+                                _stream << "      i: Cap" << pt->getIncoming()->id() << std::endl;
                         }
                     }
                 } // for p
             }
         } // for S
     }
-    stream << "Trajectory" << ((depth < 1) ? (" -- " + std::to_string(getTrajectory()->getFrameList().size()) + "F") : "")  << std::endl;
-    if (depth >= 1)
+    _stream << "Trajectory" << ((_depth < 1) ? (" -- " + std::to_string(getTrajectory()->getFrameList().size()) + "F") : "")  << std::endl;
+    if (_depth >= 1)
     {
         // Frames =======================================================================================
         for (auto F : getTrajectory()->getFrameList())
         {
-            stream << (F->isKeyOrAux() ? (F->isKey() ? "  KFrm" : " AFrm") : "  Frm") << F->id() << ((depth < 2) ? " -- " + std::to_string(F->getCaptureList().size()) + "C  " : "");
-            if (constr_by)
+            _stream << (F->isKeyOrAux() ? (F->isKey() ? "  KFrm" : " AFrm") : "  Frm") << F->id() << ((_depth < 2) ? " -- " + std::to_string(F->getCaptureList().size()) + "C  " : "");
+            if (_constr_by)
             {
-                stream << "  <-- ";
+                _stream << "  <-- ";
                 for (auto cby : F->getConstrainedByList())
-                    stream << "Fac" << cby->id() << " \t";
+                    _stream << "Fac" << cby->id() << " \t";
             }
-            stream << std::endl;
-            if (metric)
+            _stream << std::endl;
+            if (_metric)
             {
-                stream << (F->isFixed() ? "    Fix" : "    Est") << ", ts=" << std::setprecision(5)
+                _stream << (F->isFixed() ? "    Fix" : "    Est") << ", ts=" << std::setprecision(5)
                         << F->getTimeStamp();
-                stream << ",\t x = ( " << std::setprecision(2) << F->getState().transpose() << " )";
-                stream << std::endl;
+                _stream << ",\t x = ( " << std::setprecision(2) << F->getState().transpose() << " )";
+                _stream << std::endl;
             }
-            if (state_blocks)
+            if (_state_blocks)
             {
-                stream << "    sb:";
+                _stream << "    sb:";
                 for (const auto& sb : F->getStateBlockVec())
                 {
-                    stream << " " << (sb->isFixed() ? "Fix" : "Est");
+                    _stream << " " << (sb->isFixed() ? "Fix" : "Est");
                 }
-                stream << std::endl;
+                _stream << std::endl;
             }
-            // if (state_blocks)
-            // {
-            //     cout << "    sb:";
-            //     for (const auto& sb : F->getStateBlockVec())
-            //     {
-            //         cout << " " << (sb->isFixed() ? "Fix" : "Est");
-            //     }
-            //     cout << endl;
-            // }
-            if (depth >= 2)
+            if (_depth >= 2)
             {
                 // Captures =======================================================================================
                 for (auto C : F->getCaptureList())
                 {
-                    stream << "    Cap" << (C->isMotion() ? "M" : "") << C->id() << " " << C->getType();
+                    _stream << "    Cap" << (C->isMotion() ? "M" : "") << C->id() << " " << C->getType();
 
                     if(C->getSensor() != nullptr)
                     {
-                        stream << " -> Sen" << C->getSensor()->id();
+                        _stream << " -> Sen" << C->getSensor()->id();
                     }
                     else
-                        stream << " -> S-";
+                        _stream << " -> Sen-";
                     if (C->isMotion())
                     {
                         auto CM = std::static_pointer_cast<CaptureMotion>(C);
                         if (auto OC = CM->getOriginCapture())
                         {
-                            stream << " -> OCap" << OC->id();
+                            _stream << " -> OCap" << OC->id();
                             if (auto OF = OC->getFrame())
-                                stream << " ; OFrm" << OF->id();
+                                _stream << " ; OFrm" << OF->id();
                         }
                     }
 
-                    stream << ((depth < 3) ? " -- " + std::to_string(C->getFeatureList().size()) + "f" : "");
-                    if (constr_by)
+                    _stream << ((_depth < 3) ? " -- " + std::to_string(C->getFeatureList().size()) + "f" : "");
+                    if (_constr_by)
                     {
-                        stream << "  <-- ";
+                        _stream << "  <-- ";
                         for (auto cby : C->getConstrainedByList())
-                            stream << "Fac" << cby->id() << " \t";
+                            _stream << "Fac" << cby->id() << " \t";
                     }
-                    stream << std::endl;
+                    _stream << std::endl;
 
-                    if (state_blocks)
+                    if (_state_blocks)
                         for (const auto& sb : C->getStateBlockVec())
                         {
                             if(sb != nullptr)
                             {
-                                stream << "      sb: ";
-                                stream << (sb->isFixed() ? "Fix" : "Est");
-                                if (metric)
-                                    stream << std::setprecision(2) << " (" << sb->getState().transpose() << " )";
-                                stream << std::endl;
+                                _stream << "      sb: ";
+                                _stream << (sb->isFixed() ? "Fix" : "Est");
+                                if (_metric)
+                                    _stream << std::setprecision(2) << " (" << sb->getState().transpose() << " )";
+                                _stream << std::endl;
                             }
                         }
 
                     if (C->isMotion() )
                     {
                         CaptureMotionPtr CM = std::dynamic_pointer_cast<CaptureMotion>(C);
-                        stream << "      buffer size  :  " << CM->getBuffer().get().size() << std::endl;
-                        if ( metric && ! CM->getBuffer().get().empty())
+                        _stream << "      buffer size  :  " << CM->getBuffer().get().size() << std::endl;
+                        if ( _metric && ! CM->getBuffer().get().empty())
                         {
-                            stream << "      delta preint : (" << CM->getDeltaPreint().transpose() << ")" << std::endl;
+                            _stream << "      delta preint : (" << CM->getDeltaPreint().transpose() << ")" << std::endl;
                             if (CM->hasCalibration())
                             {
-                                stream << "      calib preint : (" << CM->getCalibrationPreint().transpose() << ")" << std::endl;
-                                stream << "      jacob preint : (" << CM->getJacobianCalib().row(0) << ")" << std::endl;
-                                stream << "      calib current: (" << CM->getCalibration().transpose() << ")" << std::endl;
-                                stream << "      delta correct: (" << CM->getDeltaCorrected(CM->getCalibration()).transpose() << ")" << std::endl;
+                                _stream << "      calib preint : (" << CM->getCalibrationPreint().transpose() << ")" << std::endl;
+                                _stream << "      jacob preint : (" << CM->getJacobianCalib().row(0) << ")" << std::endl;
+                                _stream << "      calib current: (" << CM->getCalibration().transpose() << ")" << std::endl;
+                                _stream << "      delta correct: (" << CM->getDeltaCorrected(CM->getCalibration()).transpose() << ")" << std::endl;
                             }
                         }
                     }
 
-                    if (depth >= 3)
+                    if (_depth >= 3)
                     {
                         // Features =======================================================================================
                         for (auto f : C->getFeatureList())
                         {
-                            stream << "      Ftr" << f->id() << " trk" << f->trackId() << " " << f->getType() << ((depth < 4) ? " -- " + std::to_string(f->getFactorList().size()) + "c  " : "");
-                            if (constr_by)
+                            _stream << "      Ftr" << f->id() << " trk" << f->trackId() << " " << f->getType() << ((_depth < 4) ? " -- " + std::to_string(f->getFactorList().size()) + "c  " : "");
+                            if (_constr_by)
                             {
-                                stream << "  <--\t";
+                                _stream << "  <--\t";
                                 for (auto cby : f->getConstrainedByList())
-                                    stream << "Fac" << cby->id() << " \t";
+                                    _stream << "Fac" << cby->id() << " \t";
                             }
-                            stream << std::endl;
-                            if (metric)
-                                stream << "        m = ( " << std::setprecision(2) << f->getMeasurement().transpose()
+                            _stream << std::endl;
+                            if (_metric)
+                                _stream << "        m = ( " << std::setprecision(2) << f->getMeasurement().transpose()
                                         << " )" << std::endl;
-                            if (depth >= 4)
+                            if (_depth >= 4)
                             {
                                 // Factors =======================================================================================
                                 for (auto c : f->getFactorList())
                                 {
-                                    stream << "        Fac" << c->id() << " " << c->getType() << " -->";
-                                    if (c->getFrameOther() == nullptr && c->getCaptureOther() == nullptr && c->getFeatureOther() == nullptr && c->getLandmarkOther() == nullptr)
-                                        stream << " Abs";
-                                    if (c->getFrameOther() != nullptr)
-                                        stream << " Frm" << c->getFrameOther()->id();
-                                    if (c->getCaptureOther() != nullptr)
-                                        stream << " Cap" << c->getCaptureOther()->id();
-                                    if (c->getFeatureOther() != nullptr)
-                                        stream << " Fac" << c->getFeatureOther()->id();
-                                    if (c->getLandmarkOther() != nullptr)
-                                        stream << " Lmk" << c->getLandmarkOther()->id();
-                                    stream << std::endl;
+                                    _stream << "        Fac" << c->id() << " " << c->getType() << " -->";
+                                    if (       c->getFrameOtherList()   .empty()
+                                            && c->getCaptureOtherList() .empty()
+                                            && c->getFeatureOtherList() .empty()
+                                            && c->getLandmarkOtherList().empty())
+                                        _stream << " Abs";
+
+                                    for (const auto& Fow : c->getFrameOtherList())
+                                        if (!Fow.expired())
+                                            _stream << " Frm" << Fow.lock()->id();
+                                    for (const auto& Cow : c->getCaptureOtherList())
+                                        if (!Cow.expired())
+                                            _stream << " Cap" << Cow.lock()->id();
+                                    for (const auto& fow : c->getFeatureOtherList())
+                                        if (!fow.expired())
+                                            _stream << " Ftr" << fow.lock()->id();
+                                    for (const auto& Low : c->getLandmarkOtherList())
+                                        if (!Low.expired())
+                                            _stream << " Lmk" << Low.lock()->id();
+                                    _stream << std::endl;
                                 } // for c
                             }
                         } // for f
@@ -1154,236 +1153,208 @@ void Problem::print(int depth, std::ostream& stream, bool constr_by, bool metric
             }
         } // for F
     }
-    stream << "Map" << ((depth < 1) ? ("        -- " + std::to_string(getMap()->getLandmarkList().size()) + "L") : "") << std::endl;
-    if (depth >= 1)
+    _stream << "Map" << ((_depth < 1) ? ("        -- " + std::to_string(getMap()->getLandmarkList().size()) + "L") : "") << std::endl;
+    if (_depth >= 1)
     {
         // Landmarks =======================================================================================
         for (auto L : getMap()->getLandmarkList())
         {
-            stream << "  Lmk" << L->id() << " " << L->getType();
-            if (constr_by)
+            _stream << "  Lmk" << L->id() << " " << L->getType();
+            if (_constr_by)
             {
-                stream << "\t<-- ";
+                _stream << "\t<-- ";
                 for (auto cby : L->getConstrainedByList())
-                    stream << "Fac" << cby->id() << " \t";
+                    _stream << "Fac" << cby->id() << " \t";
             }
-            stream << std::endl;
-            if (metric)
+            _stream << std::endl;
+            if (_metric)
             {
-                stream << (L->isFixed() ? "    Fix" : "    Est");
-                stream << ",\t x = ( " << std::setprecision(2) << L->getState().transpose() << " )";
-                stream << std::endl;
+                _stream << (L->isFixed() ? "    Fix" : "    Est");
+                _stream << ",\t x = ( " << std::setprecision(2) << L->getState().transpose() << " )";
+                _stream << std::endl;
             }
-            if (state_blocks)
+            if (_state_blocks)
             {
-                stream << "    sb:";
+                _stream << "    sb:";
                 for (const auto& sb : L->getStateBlockVec())
                 {
                     if (sb != nullptr)
-                        stream << (sb->isFixed() ? " Fix" : " Est");
+                        _stream << (sb->isFixed() ? " Fix" : " Est");
                 }
-                stream << std::endl;
+                _stream << std::endl;
             }
         } // for L
     }
-    stream << "-----------------------------------------" << std::endl;
-    stream << std::endl;
+    _stream << "-----------------------------------------" << std::endl;
+    _stream << std::endl;
 }
 
-bool Problem::check(bool verbose, std::ostream& stream) const
+bool Problem::check(bool _verbose, std::ostream& _stream) const
 {
 
     CheckLog log(true, "");
     log.explanation_ = "## WOLF::problem inconsistencies list \n   ---------------------------------- \n";
 
-    if (verbose) stream << std::endl;
-    if (verbose) stream << "Wolf tree integrity ---------------------" << std::endl;
-    auto P_raw = this;
-    if (verbose)
+    if (_verbose) _stream << std::endl;
+    if (_verbose) _stream << "Wolf tree integrity ---------------------" << std::endl;
+    auto P = shared_from_this();
+    if (_verbose)
     {
-        stream << "Prb @ " << P_raw << std::endl;
+        _stream << "Prb @ " << P.get() << std::endl;
     }
     // ------------------------
     //     HARDWARE branch
     // ------------------------
     auto H = hardware_ptr_;
-    if (verbose)
+    if (_verbose)
     {
-        stream << "Hrw @ " << H.get() << std::endl;
+        _stream << "Hrw @ " << H.get() << std::endl;
     }
-    // check pointer to Problem
-    // is_consistent = is_consistent && (H->getProblem().get() == P_raw);
 
+    // check pointer to Problem
     std::stringstream inconsistency_explanation;
     inconsistency_explanation << "Hardware problem pointer is " << H->getProblem().get()
-        << " but problem pointer is " << P_raw << "\n";
-    log.compose(CheckLog((H->getProblem().get() == P_raw), inconsistency_explanation.str()));
-    //Clear inconsistency_explanation
-    std::stringstream().swap(inconsistency_explanation);
+        << " but problem pointer is " << P.get() << "\n";
+    log.assertTrue((H->getProblem() == P), inconsistency_explanation);
+
 
     // Sensors =======================================================================================
     for (auto S : H->getSensorList())
     {
-        if (verbose)
+        if (_verbose)
         {
-            stream << "  Sen" << S->id() << " @ " << S.get() << std::endl;
-            stream << "    -> Prb @ " << S->getProblem().get() << std::endl;
-            stream << "    -> Hrw @ " << S->getHardware().get() << std::endl;
+            _stream << "  Sen" << S->id() << " @ " << S.get() << std::endl;
+            _stream << "    -> Prb @ " << S->getProblem().get() << std::endl;
+            _stream << "    -> Hrw @ " << S->getHardware().get() << std::endl;
             for (auto pair: S->getStateBlockMap())
             {
                 auto sb = pair.second;
-                stream <<  "    " << pair.first << " sb @ " << sb.get();
+                _stream <<  "    " << pair.first << " sb @ " << sb.get();
                 if (sb)
                 {
                     auto lp = sb->getLocalParametrization();
                     if (lp)
-                        stream <<  " (lp @ " << lp.get() << ")";
+                        _stream <<  " (lp @ " << lp.get() << ")";
                 }
-                stream << std::endl;
+                _stream << std::endl;
             }
         }
+
         // check problem and hardware pointers
-        // is_consistent = is_consistent && (S->getProblem().get() == P_raw);
         inconsistency_explanation << "Sensor problem pointer is " << S->getProblem().get()
-            << " but problem pointer is " << P_raw << "\n";
-        log.compose(CheckLog((S->getProblem().get() == P_raw), inconsistency_explanation.str()));
-        //Clear inconsistency_explanation
-        std::stringstream().swap(inconsistency_explanation);
+            << " but problem pointer is " << P.get() << "\n";
+        log.assertTrue((S->getProblem() == P), inconsistency_explanation);
+
 
-        //  is_consistent = is_consistent && (S->getHardware() == H);
         inconsistency_explanation << "Sensor hardware pointer is " << S->getHardware()
             << " but hardware pointer is " << H << "\n";
-        log.compose(CheckLog((S->getHardware() == H), inconsistency_explanation.str()));
-        //Clear inconsistency_explanation
-        std::stringstream().swap(inconsistency_explanation);
+        log.assertTrue((S->getHardware() == H), inconsistency_explanation);
+
 
         //  Processors =======================================================================================
         for (auto p : S->getProcessorList())
         {
-            if (verbose)
+            if (_verbose)
             {
-                stream << "    Prc" << p->id() << " @ " << p.get() << " -> Sen" << p->getSensor()->id() << std::endl;
-                stream << "      -> Prb  @ " << p->getProblem().get() << std::endl;
-                stream << "      -> Sen" << p->getSensor()->id() << " @ " << p->getSensor().get() << std::endl;
+                _stream << "    Prc" << p->id() << " @ " << p.get() << " -> Sen" << p->getSensor()->id() << std::endl;
+                _stream << "      -> Prb  @ " << p->getProblem().get() << std::endl;
+                _stream << "      -> Sen" << p->getSensor()->id() << " @ " << p->getSensor().get() << std::endl;
             }
-            // check problem and sensor pointers
-
-            //  is_consistent = is_consistent && (p->getProblem().get() == P_raw);
 
+            // check problem and sensor pointers
             inconsistency_explanation << "Processor problem pointer is " << p->getProblem().get()
-                << " but problem pointer is " << P_raw << "\n";
-            log.compose(CheckLog((p->getProblem().get() == P_raw), inconsistency_explanation.str()));
-            //Clear inconsistency_explanation
-            std::stringstream().swap(inconsistency_explanation);
+                << " but problem pointer is " << P.get() << "\n";
+            log.assertTrue((p->getProblem() == P), inconsistency_explanation);
 
-            // is_consistent = is_consistent && (p->getSensor() == S);
 
             inconsistency_explanation << "Processor sensor pointer is " << p->getSensor()
-                << " but sensor pointer is " << P_raw << "\n";
-            log.compose(CheckLog((p->getProblem().get() == P_raw), inconsistency_explanation.str()));
-            //Clear inconsistency_explanation
-            std::stringstream().swap(inconsistency_explanation);
+                << " but sensor pointer is " << P.get() << "\n";
+            log.assertTrue((p->getProblem() == P), inconsistency_explanation);
+
         }
     }
     // ------------------------
     //    TRAJECTORY branch
     // ------------------------
     auto T = trajectory_ptr_;
-    if (verbose)
+    if (_verbose)
     {
-        stream << "Trj @ " << T.get() << std::endl;
+        _stream << "Trj @ " << T.get() << std::endl;
     }
-    // check pointer to Problem
-    // is_consistent = is_consistent && (T->getProblem().get() == P_raw);
-
 
+    // check pointer to Problem
     inconsistency_explanation << "Trajectory problem pointer is " << T->getProblem().get()
-       << " but problem pointer is" << P_raw << "\n";
-    log.compose(CheckLog((T->getProblem().get() == P_raw), inconsistency_explanation.str()));
-    //Clear inconsistency_explanation
-    std::stringstream().swap(inconsistency_explanation);
+       << " but problem pointer is" << P.get() << "\n";
+    log.assertTrue((T->getProblem() == P), inconsistency_explanation);
+
 
     // Frames =======================================================================================
     for (auto F : T->getFrameList())
     {
-      if (verbose) {
-        stream << (F->isKeyOrAux() ? (F->isKey() ? "  KFrm" : " EFrm") : "  Frm")
+      if (_verbose) {
+        _stream << (F->isKeyOrAux() ? (F->isKey() ? "  KFrm" : " EFrm") : "  Frm")
              << F->id() << " @ " << F.get() << std::endl;
-        stream << "    -> Prb @ " << F->getProblem().get() << std::endl;
-        stream << "    -> Trj @ " << F->getTrajectory().get() << std::endl;
+        _stream << "    -> Prb @ " << F->getProblem().get() << std::endl;
+        _stream << "    -> Trj @ " << F->getTrajectory().get() << std::endl;
       }
       for (const auto &pair: F->getStateBlockMap()) {
+
           auto sb = pair.second;
-          inconsistency_explanation << "Frame's " << F.get()
+
+          // check for valid state block
+          inconsistency_explanation << "Frame " << F->id() << " @ "<< F.get()
                                   << " has State block pointer " << sb.get()
-                                  << " null! \n";
-          log.compose(
-              CheckLog((sb.get() != 0), inconsistency_explanation.str()));
-          // Clear inconsistency_explanation
-          std::stringstream().swap(inconsistency_explanation);
-          if (verbose) {
-            stream << "    "<< pair.first << " sb @ " << sb.get();
+                                  << " = 0 \n";
+          log.assertTrue((sb.get() != 0), inconsistency_explanation);
+
+          if (_verbose) {
+            _stream << "    "<< pair.first << " sb @ " << sb.get();
             if (sb) {
               auto lp = sb->getLocalParametrization();
               if (lp)
-                stream << " (lp @ " << lp.get() << ")";
+                _stream << " (lp @ " << lp.get() << ")";
             }
-            stream << std::endl;
+            _stream << std::endl;
           }
       }
 
-        // check problem and trajectory pointers
-        // is_consistent = is_consistent && (F->getProblem().get() == P_raw);
-
+        // check problem pointer
         inconsistency_explanation << "Frame problem pointer is " << F->getProblem().get()
-        << " but problem pointer is" << P_raw << "\n";
-        log.compose(CheckLog((F->getProblem().get() == P_raw), inconsistency_explanation.str()));
-        //Clear inconsistency_explanation
-        std::stringstream().swap(inconsistency_explanation);
-
-        // is_consistent = is_consistent && (F->getTrajectory() == T);
+                        << " but problem pointer is" << P.get() << "\n";
+        log.assertTrue((F->getProblem() == P), inconsistency_explanation);
 
+        // check trajectory pointer
         inconsistency_explanation << "Frame trajectory pointer is " << F->getTrajectory()
-        << " but trajectory pointer is" << T << "\n";
-        log.compose(CheckLog((F->getTrajectory() == T), inconsistency_explanation.str()));
-        //Clear inconsistency_explanation
-        std::stringstream().swap(inconsistency_explanation);
+                        << " but trajectory pointer is" << T << "\n";
+        log.assertTrue((F->getTrajectory() == T), inconsistency_explanation);
 
+
+        // check constrained_by
         for (auto cby : F->getConstrainedByList())
         {
-          for (auto sb : cby->getStateBlockPtrVector()) {
-            inconsistency_explanation
-                << "Factor " << cby.get() << " constraining " << F.get()
-                << " has State block pointer " << sb.get() << " null! \n";
-            log.compose(
-                CheckLog((sb.get() != 0), inconsistency_explanation.str()));
-            // Clear inconsistency_explanation
-            std::stringstream().swap(inconsistency_explanation);
-          }
-          if (verbose) {
-            stream << "    <- c" << cby->id() << " -> Frm"
-                 << cby->getFrameOther()->id() << std::endl;
-          }
-            // check constrained_by pointer to this frame
-            // is_consistent = is_consistent && (cby->getFrameOther() == F);
+            if (_verbose)
+            {
+                _stream << "    <- c" << cby->id() << " -> ";
+                for (const auto& Fow : cby->getFrameOtherList())
+                    _stream << " F" << Fow.lock()->id() << std::endl;
+            }
 
-            inconsistency_explanation << "constrained-by frame pointer is " << cby->getFrameOther()
-            << " but frame pointer is" << F << "\n";
-            log.compose(CheckLog((cby->getFrameOther() == F), inconsistency_explanation.str()));
-            //Clear inconsistency_explanation
-            std::stringstream().swap(inconsistency_explanation);
+            // check constrained_by pointer to this frame
+            inconsistency_explanation << "constrained-by frame " << F->id() << " @ " << F
+                                << " not found among constrained-by factors\n";
+            log.assertTrue((cby->hasFrameOther(F)), inconsistency_explanation);
 
             for (auto sb : cby->getStateBlockPtrVector())
             {
 
-              if (verbose) {
-                stream << "      sb @ " << sb.get();
+              if (_verbose) {
+                _stream << "      sb @ " << sb.get();
                 if (sb) {
                   auto lp = sb->getLocalParametrization();
                   if (lp)
-                    stream << " (lp @ " << lp.get() << ")";
+                    _stream << " (lp @ " << lp.get() << ")";
                 }
-                stream << std::endl;
+                _stream << std::endl;
               }
             }
         }
@@ -1391,361 +1362,383 @@ bool Problem::check(bool verbose, std::ostream& stream) const
         // Captures =======================================================================================
         for (auto C : F->getCaptureList())
         {
-            if (verbose)
+            if (_verbose)
             {
-                stream << "    Cap" << C->id() << " @ " << C.get() << " -> Sen";
-                if (C->getSensor()) stream << C->getSensor()->id();
-                else stream << "-";
-                stream << std::endl;
-                stream << "      -> Prb  @ " << C->getProblem().get() << std::endl;
-                stream << "      -> Frm" << C->getFrame()->id() << " @ " << C->getFrame().get() << std::endl;
+                _stream << "    Cap" << C->id() << " @ " << C.get() << " -> Sen";
+                if (C->getSensor()) _stream << C->getSensor()->id();
+                else _stream << "-";
+                _stream << std::endl;
+                _stream << "      -> Prb  @ " << C->getProblem().get() << std::endl;
+                _stream << "      -> Frm" << C->getFrame()->id() << " @ " << C->getFrame().get() << std::endl;
             }
-                for (auto pair: C->getStateBlockMap())
+            for (auto pair: C->getStateBlockMap())
+            {
+                auto sb = pair.second;
+
+                // check for valid state block
+                inconsistency_explanation << "Capture " << C->id() << " @ " << C.get() << " has State block pointer "
+                                          << sb.get() << " = 0 \n";
+                log.assertTrue((sb.get() != 0), inconsistency_explanation);
+
+                if (_verbose)
                 {
-                    auto sb = pair.second;
-                    if (verbose)
-                    {
-                    stream <<  "      " << pair.first << " sb @ " << sb.get();
+                    _stream <<  "      " << pair.first << " sb @ " << sb.get();
                     if (sb) {
-                      auto lp = sb->getLocalParametrization();
-                      if (lp)
-                        stream << " (lp @ " << lp.get() << ")";
-                    }
-                    stream << std::endl;
+                        auto lp = sb->getLocalParametrization();
+                        if (lp)
+                            _stream << " (lp @ " << lp.get() << ")";
                     }
+                    _stream << std::endl;
                 }
+            }
 
             // check problem and frame pointers
-            // is_consistent = is_consistent && (C->getProblem().get() == P_raw);
-
             inconsistency_explanation << "Capture problem pointer is " << C->getProblem().get()
-            << " but problem pointer is" << P_raw << "\n";
-            log.compose(CheckLog((C->getProblem().get() == P_raw), inconsistency_explanation.str()));
-            //Clear inconsistency_explanation
-            std::stringstream().swap(inconsistency_explanation);
+            << " but problem pointer is" << P.get() << "\n";
+            log.assertTrue((C->getProblem() == P), inconsistency_explanation);
 
-            // is_consistent = is_consistent && (C->getFrame() == F);
 
             inconsistency_explanation << "Capture frame pointer is " << C->getFrame()
             << " but frame pointer is" << F << "\n";
-            log.compose(CheckLog((C->getFrame() == F), inconsistency_explanation.str()));
-            //Clear inconsistency_explanation
-            std::stringstream().swap(inconsistency_explanation);
+            log.assertTrue((C->getFrame() == F), inconsistency_explanation);
+
+
+            // check contrained_by
+            for (const auto& cby : C->getConstrainedByList())
+            {
+                if (_verbose)
+                {
+                    _stream << "      <- c" << cby->id() << " -> ";
+                    for (const auto& Cow : cby->getCaptureOtherList())
+                        _stream << " C" << Cow.lock()->id();
+                    _stream << std::endl;
+                }
+
+                // check constrained_by pointer to this capture
+                inconsistency_explanation << "constrained by capture " << C->id() << " @ " << C
+                                          << " not found among constrained-by factors\n";
+                log.assertTrue((cby->hasCaptureOther(C)), inconsistency_explanation);
+
+                for (auto sb : cby->getStateBlockPtrVector())
+                {
+                    if (_verbose)
+                    {
+                        _stream << "      sb @ " << sb.get();
+                        if (sb)
+                        {
+                            auto lp = sb->getLocalParametrization();
+                            if (lp)
+                                _stream <<  " (lp @ " << lp.get() << ")";
+                        }
+                        _stream << std::endl;
+                    }
+                }
+
+            }
 
             // Features =======================================================================================
             for (auto f : C->getFeatureList())
             {
-                if (verbose)
+                if (_verbose)
                 {
-                    stream << "      Ftr" << f->id() << " @ " << f.get() << std::endl;
-                    stream << "        -> Prb  @ " << f->getProblem().get() << std::endl;
-                    stream << "        -> Cap" << f->getCapture()->id() << " @ " << f->getCapture().get()
+                    _stream << "      Ftr" << f->id() << " @ " << f.get() << std::endl;
+                    _stream << "        -> Prb  @ " << f->getProblem().get() << std::endl;
+                    _stream << "        -> Cap" << f->getCapture()->id() << " @ " << f->getCapture().get()
                             << std::endl;
                 }
-                // check problem and capture pointers
-                // is_consistent = is_consistent && (f->getProblem().get() == P_raw);
 
+                // check problem and capture pointers
                 inconsistency_explanation << "Feature frame pointer is " << f->getProblem().get()
-                << " but problem pointer is" << P_raw << "\n";
-                log.compose(CheckLog((f->getProblem().get() == P_raw), inconsistency_explanation.str()));
-                //Clear inconsistency_explanation
-                std::stringstream().swap(inconsistency_explanation);
+                << " but problem pointer is" << P.get() << "\n";
+                log.assertTrue((f->getProblem() == P), inconsistency_explanation);
 
-                // is_consistent = is_consistent && (f->getCapture() == C);
 
                 inconsistency_explanation << "Feature capture pointer is " << f->getCapture()
                 << " but capture pointer is" << C << "\n";
-                log.compose(CheckLog((f->getCapture() == C), inconsistency_explanation.str()));
-                //Clear inconsistency_explanation
-                std::stringstream().swap(inconsistency_explanation);
+                log.assertTrue((f->getCapture() == C), inconsistency_explanation);
 
+
+                // check contrained_by
                 for (auto cby : f->getConstrainedByList())
                 {
-                    if (verbose)
+                    if (_verbose)
                     {
-                        stream << "     <- c" << cby->id() << " -> Ftr" << cby->getFeatureOther()->id() << std::endl;
+                        _stream << "        <- c" << cby->id() << " -> ";
+                        for (const auto& fow : cby->getFeatureOtherList())
+                            _stream << " f" << fow.lock()->id();
+                        _stream << std::endl;
                     }
+
                     // check constrained_by pointer to this feature
-                    // is_consistent = is_consistent && (cby->getFeatureOther() == f);
+                    inconsistency_explanation << "constrained by Feature " << f->id() << " @ " << f
+                                                << " not found among constrained-by factors\n";
+                    log.assertTrue((cby->hasFeatureOther(f)), inconsistency_explanation);
 
-                    inconsistency_explanation << "constrained by Feature pointer is " << cby->getFeatureOther()
-                    << " but feature pointer is" << f << "\n";
-                    log.compose(CheckLog((cby->getFeatureOther() == f), inconsistency_explanation.str()));
-                    //Clear inconsistency_explanation
-                    std::stringstream().swap(inconsistency_explanation);
                 }
 
                 // Factors =======================================================================================
                 for (auto c : f->getFactorList())
                 {
-                    if (verbose)
-                        stream << "        Fac" << c->id() << " @ " << c.get();
+                    if (_verbose)
+                        _stream << "        Fac" << c->id() << " @ " << c.get();
 
-                    auto Fo = c->getFrameOther();
-                    auto Co = c->getCaptureOther();
-                    auto fo = c->getFeatureOther();
-                    auto Lo = c->getLandmarkOther();
-
-                    if ( !Fo && !Co && !fo && !Lo )    // case ABSOLUTE:
+                    if (       c->getFrameOtherList()   .empty()
+                            && c->getCaptureOtherList() .empty()
+                            && c->getFeatureOtherList() .empty()
+                            && c->getLandmarkOtherList().empty() )    // case ABSOLUTE:
                     {
-                        if (verbose)
-                            stream << " --> Abs." << std::endl;
+                        if (_verbose)
+                            _stream << " --> Abs.";
                     }
 
                     // find constrained_by pointer in constrained frame
-                    if ( Fo )  // case FRAME:
+                    for (const auto& Fow : c->getFrameOtherList())
                     {
-                        if (verbose)
-                            stream << " ( --> Frm" << Fo->id() << " <- ";
-                        bool found = false;
-                        for (auto cby : Fo->getConstrainedByList())
+                        if (!Fow.expired())
                         {
-                            if (verbose)
-                                stream << " Fac" << cby->id();
-                            found = found || (c == cby);
-                        }
-                        if (verbose)
-                            stream << ")";
-                        // check constrained_by pointer in constrained frame
-                        // is_consistent = is_consistent && found;
+                            const auto& Fo = Fow.lock();
+                            if (_verbose)
+                            {
+                                _stream << " ( --> F" << Fo->id() << " <- ";
+                                for (auto cby : Fo->getConstrainedByList())
+                                    _stream << " c" << cby->id();
+                            }
 
-                        inconsistency_explanation << "The constrained Feature " << Fo
-                            << " does not close the constrained-by loop start =  " << c << "\n";
-                        log.compose(CheckLog((found), inconsistency_explanation.str()));
-                        //Clear inconsistency_explanation
-                        std::stringstream().swap(inconsistency_explanation);
+                            // check constrained_by pointer in constrained frame
+                            bool found = Fo->isConstrainedBy(c);
+                            inconsistency_explanation << "The constrained Feature " << Fo->id() << " @ " << Fo
+                                    << " not found among constrained-by factors\n";
+                            log.assertTrue((found), inconsistency_explanation);
 
+                        }
                     }
+                    if (_verbose && !c->getFrameOtherList().empty())
+                        _stream << ")";
 
                     // find constrained_by pointer in constrained capture
-                    if ( Co )  // case CAPTURE:
+                    for (const auto& Cow : c->getCaptureOtherList())
                     {
-                        if (verbose)
-                            stream << " ( --> Cap" << Co->id() << " <- ";
-                        bool found = false;
-                        for (auto cby : Co->getConstrainedByList())
+                        if (!Cow.expired())
                         {
-                            if (verbose)
-                                stream << " Fac" << cby->id();
-                            found = found || (c == cby);
-                        }
-                        if (verbose)
-                            stream << ")";
-                        // check constrained_by pointer in constrained frame
-                        // is_consistent = is_consistent && found;
+                            const auto& Co = Cow.lock();
+
+                            if (_verbose)
+                            {
+                                _stream << " ( --> C" << Co->id() << " <- ";
+                                for (auto cby : Co->getConstrainedByList())
+                                    _stream << " c" << cby->id();
+                            }
 
-                        inconsistency_explanation << "The constrained capture " << Co
-                            << " does not close the constrained-by loop start =  " << c << "\n";
-                        log.compose(CheckLog((found), inconsistency_explanation.str()));
-                        //Clear inconsistency_explanation
-                        std::stringstream().swap(inconsistency_explanation);
+                            // check constrained_by pointer in constrained frame
+                            bool found = Co->isConstrainedBy(c);
+                            inconsistency_explanation << "The constrained capture " << Co->id() << " @ " << Co
+                                    << " not found among constrained-by factors\n";
+                            log.assertTrue((found), inconsistency_explanation);
 
+                        }
                     }
+                    if (_verbose && !c->getCaptureOtherList().empty())
+                        _stream << ")";
 
                     // find constrained_by pointer in constrained feature
-                    if ( fo )   // case FEATURE:
+                    for (const auto& fow : c->getFeatureOtherList())
                     {
-                        if (verbose)
-                            stream << " ( --> Ftr" << fo->id() << " <- ";
-                        bool found = false;
-                        for (auto cby : fo->getConstrainedByList())
+                        if (!fow.expired())
                         {
-                            if (verbose)
-                                stream << " Fac" << cby->id();
-                            found = found || (c == cby);
+                            const auto& fo = fow.lock();
+                            if (_verbose)
+                            {
+                                _stream << " ( --> f" << fo->id() << " <- ";
+                                for (auto cby : fo->getConstrainedByList())
+                                    _stream << " c" << cby->id();
+                            }
+
+                            // check constrained_by pointer in constrained feature
+                            bool found = fo->isConstrainedBy(c);
+                            inconsistency_explanation << "The constrained feature " << fo->id() << " @ " << fo
+                                                      << " not found among constrained-by factors\n";
+                            log.assertTrue((found), inconsistency_explanation);
                         }
-                        if (verbose)
-                            stream << ")";
-                        // check constrained_by pointer in constrained feature
-                        // is_consistent = is_consistent && found;
-
-                        inconsistency_explanation << "The constrained feature" << fo
-                            << " does not close the constrained-by loop start =  " << c << "\n";
-                        log.compose(CheckLog((found), inconsistency_explanation.str()));
-                        //Clear inconsistency_explanation
-                        std::stringstream().swap(inconsistency_explanation);
                     }
+                    if (_verbose && !c->getFeatureOtherList().empty())
+                        _stream << ")";
 
                     // find constrained_by pointer in constrained landmark
-                    if ( Lo )      // case LANDMARK:
+                    for (const auto& Low : c->getLandmarkOtherList())
                     {
-                        if (verbose)
-                            stream << " ( --> Lmk" << Lo->id() << " <- ";
-                        bool found = false;
-                        for (auto cby : Lo->getConstrainedByList())
+                        if (Low.expired())
                         {
-                            if (verbose)
-                                stream << " Fac" << cby->id();
-                            found = found || (c == cby);
+                            const auto& Lo = Low.lock();
+
+                            if (_verbose)
+                            {
+                                _stream << " ( --> L" << Lo->id() << " <- ";
+                                for (auto cby : Lo->getConstrainedByList())
+                                    _stream << " c" << cby->id();
+                            }
+
+                            // check constrained_by pointer in constrained landmark
+                            bool found = Lo->isConstrainedBy(c);
+                            inconsistency_explanation << "The constrained landmark " << Lo->id() << " @ " << Lo
+                                    << " not found among constrained-by factors\n";
+                            log.assertTrue((found), inconsistency_explanation);
+
                         }
-                        if (verbose)
-                            stream << ")";
-                        // check constrained_by pointer in constrained landmark
-                        // is_consistent = is_consistent && found;
-
-                        inconsistency_explanation << "The constrained landmark " << Lo
-                            << " does not close the constrained-by loop start =  " << c << "\n";
-                        log.compose(CheckLog((found), inconsistency_explanation.str()));
-                        //Clear inconsistency_explanation
-                        std::stringstream().swap(inconsistency_explanation);
                     }
-                    if (verbose)
-                        stream << std::endl;
+                    if (_verbose && !c->getLandmarkOtherList().empty())
+                        _stream << ")";
 
-                    if (verbose)
+                    if (_verbose)
+                        _stream << std::endl;
+
+                    if (_verbose)
                     {
-                        stream << "          -> Prb  @ " << c->getProblem().get() << std::endl;
-                        stream << "          -> Ftr" << c->getFeature()->id() << " @ " << c->getFeature().get() << std::endl;
+                        _stream << "          -> Prb  @ " << c->getProblem().get() << std::endl;
+                        _stream << "          -> Ftr" << c->getFeature()->id() << " @ " << c->getFeature().get() << std::endl;
                     }
-                    // check problem and feature pointers
-                    // is_consistent = is_consistent && (c->getProblem().get() == P_raw);
 
-                    inconsistency_explanation << "The factor " << c << " has problem ptr " << c->getProblem().get()
-                        << " but problem ptr is " << P_raw << "\n";
-                    log.compose(CheckLog((c->getProblem().get() == P_raw), inconsistency_explanation.str()));
-                    //Clear inconsistency_explanation
-                    std::stringstream().swap(inconsistency_explanation);
+                    // check problem and feature pointers
+                    inconsistency_explanation << "The factor " << c->id() << " @ " << c << " has problem ptr " << c->getProblem().get()
+                        << " but problem ptr is " << P.get() << "\n";
+                    log.assertTrue((c->getProblem() == P), inconsistency_explanation);
 
-                    // is_consistent = is_consistent && (c->getFeature() == f);
 
-                    inconsistency_explanation << "The factor " << c << " has feature ptr " << c->getFeature()
+                    inconsistency_explanation << "The factor " << c->id() << " @ " << c << " has feature ptr " << c->getFeature()
                         << " but it should have " << f << "\n";
-                    log.compose(CheckLog((c->getProblem().get() == P_raw), inconsistency_explanation.str()));
-                    //Clear inconsistency_explanation
-                    std::stringstream().swap(inconsistency_explanation);
+                    log.assertTrue((c->getProblem() == P), inconsistency_explanation);
+
 
                     // find state block pointers in all constrained nodes
                     SensorBasePtr S = c->getFeature()->getCapture()->getSensor(); // get own sensor to check sb
                     for (auto sb : c->getStateBlockPtrVector())
                     {
                         bool found = false;
-                        if (verbose)
+                        if (_verbose)
                         {
-                            stream <<  "          sb @ " << sb.get();
+                            _stream <<  "          sb @ " << sb.get();
                             if (sb)
                             {
                                 auto lp = sb->getLocalParametrization();
                                 if (lp)
-                                    stream <<  " (lp @ " << lp.get() << ")";
+                                    _stream <<  " (lp @ " << lp.get() << ")";
                             }
                         }
                         bool found_here;
-                        std::vector<StateBlockPtr> sb_vec;
 
                         // find in own Frame
-                        sb_vec          = F->getStateBlockVec();
-                        found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                        if (found_here) stream << " F" << F->id();
+                        found_here  = F->hasStateBlock(sb);
+                        if (found_here && _verbose) _stream << " F" << F->id();
                         found       = found || found_here;
 
                         // find in own Capture
-                        sb_vec          = C->getStateBlockVec();
-                        found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                        if (found_here) stream << " C" << C->id();
+                        found_here  = C->hasStateBlock(sb);
+                        if (found_here && _verbose) _stream << " C" << C->id();
                         found       = found || found_here;
 
                         // Find in other Captures of the own Frame
                         if (!found_here)
                             for (auto FC : F->getCaptureList())
                             {
-                                sb_vec          = FC->getStateBlockVec();
-                                found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                                if (found_here) stream << " F" << F->id() << ".C" << FC->id();
+                                found_here  = FC->hasStateBlock(sb);
+                                if (found_here && _verbose) _stream << " F" << F->id() << ".C" << FC->id();
                                 found       = found || found_here;
                             }
 
                         // find in own Sensor
                         if (S)
                         {
-                            sb_vec          = S->getStateBlockVec();
-                            found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                            if (found_here) stream << " S" << S->id();
+                            found_here  = S->hasStateBlock(sb);
+                            if (found_here && _verbose) _stream << " S" << S->id();
                             found       = found || found_here;
                         }
 
+
                         // find in constrained Frame
-                        if (Fo){
-                            sb_vec          = Fo->getStateBlockVec();
-                            found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                            if (found_here) stream << " Fo" << Fo->id();
-                            found       = found || found_here;
+                        for (const auto& Fow : c->getFrameOtherList())
+                        {
+                            if (!Fow.expired())
+                            {
+                                const auto& Fo = Fow.lock();
+                                found_here  = Fo->hasStateBlock(sb);
+                                if (found_here && _verbose) _stream << " Fo" << Fo->id();
+                                found       = found || found_here;
+
+                                // find in feature other's captures
+                                for (auto FoC : Fo->getCaptureList())
+                                {
+                                    found_here  = FoC->hasStateBlock(sb);
+                                    if (found_here && _verbose) _stream << " Fo" << Fo->id() << ".C" << FoC->id();
+                                    found       = found || found_here;
+                                }
 
+                            }
                         }
 
                         // find in constrained Capture
-                        if (Co)
+                        for (const auto& Cow : c->getCaptureOtherList())
                         {
-                            sb_vec          = Co->getStateBlockVec();
-                            found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                            if (found_here) stream << " Co" << Co->id();
-                            found       = found || found_here;
-                        }
-
-                        // Find in other Captures of the constrained Frame
-                        if (!found_here && Fo)
-                            for (auto FoC : Fo->getCaptureList())
+                            if (!Cow.expired())
                             {
-                                sb_vec          = FoC->getStateBlockVec();
-                                found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                                if (found_here) stream << " Fo" << Fo->id() << ".C" << FoC->id();
+                                const auto& Co = Cow.lock();
+                                found_here  = Co->hasStateBlock(sb);
+                                if (found_here && _verbose) _stream << " Co" << Co->id();
                                 found       = found || found_here;
                             }
+                        }
 
                         // find in constrained Feature
-                        if (fo)
+                        for (const auto& fow : c->getFeatureOtherList())
                         {
-                            // find in constrained feature's Frame
-                            auto foF    = fo->getFrame();
-                            sb_vec          = foF->getStateBlockVec();
-                            found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                            if (found_here) stream << " foF" << foF->id();
-                            found       = found || found_here;
+                            if (!fow.expired())
+                            {
+                                const auto& fo = fow.lock();
+                                // find in constrained feature's Frame
+                                auto foF    = fo->getFrame();
+                                found_here  = foF->hasStateBlock(sb);
+                                if (found_here && _verbose) _stream << " foF" << foF->id();
+                                found       = found || found_here;
 
-                            // find in constrained feature's Capture
-                            auto foC    = fo->getCapture();
-                            sb_vec          = foC->getStateBlockVec();
-                            found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                            if (found_here) stream << " foC" << foC->id();
-                            found       = found || found_here;
+                                // find in constrained feature's Capture
+                                auto foC    = fo->getCapture();
+                                found_here  = foC->hasStateBlock(sb);
+                                if (found_here && _verbose) _stream << " foC" << foC->id();
+                                found       = found || found_here;
 
-                            // find in constrained feature's Sensor
-                            auto foS    = fo->getCapture()->getSensor();
-                            sb_vec          = foS->getStateBlockVec();
-                            found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                            if (found_here) stream << " foS" << foS->id();
-                            found       = found || found_here;
+                                // find in constrained feature's Sensor
+                                auto foS    = fo->getCapture()->getSensor();
+                                found_here  = foS->hasStateBlock(sb);
+                                if (found_here && _verbose) _stream << " foS" << foS->id();
+                                found       = found || found_here;
+                            }
                         }
 
                         // find in constrained landmark
-                        if (Lo)
+                        for (const auto& Low : c->getLandmarkOtherList())
                         {
-                            sb_vec          = Lo->getStateBlockVec();
-                            found_here      = (std::find(sb_vec.begin(), sb_vec.end(), sb) != sb_vec.end());
-                            if (found_here) stream << " Lo" << Lo->id();
-                            found       = found || found_here;
+                            if (!Low.expired())
+                            {
+                                const auto& Lo = Low.lock();
+                                found_here  = Lo->hasStateBlock(sb);
+                                if (found_here && _verbose) _stream << " Lo" << Lo->id();
+                                found       = found || found_here;
+                            }
                         }
 
-                        if (verbose)
+                        if (_verbose)
                         {
                             if (found)
-                                stream << " found";
+                                _stream << " found";
                             else
-                                stream << " NOT FOUND !";
-                            stream << std::endl;
+                                _stream << " NOT FOUND !";
+                            _stream << std::endl;
                         }
 
+                        // check that the state block has been found somewhere
                         inconsistency_explanation << "The stateblock " << sb << " has not been found (is floating!)";
-                        log.compose(CheckLog((found), inconsistency_explanation.str()));
-                        //Clear inconsistency_explanation
-                        std::stringstream().swap(inconsistency_explanation);
-
-                        inconsistency_explanation << "The stateblock " << sb << " of factor " << c << " is null\n";
-                        log.compose(CheckLog((sb.get() != nullptr), inconsistency_explanation.str()));
-                        //Clear inconsistency_explanation
-                        std::stringstream().swap(inconsistency_explanation);
+                        log.assertTrue((found), inconsistency_explanation);
 
-                        // check that all state block pointers were found
-                        // is_consistent = is_consistent && found;
+                        inconsistency_explanation << "The stateblock " << sb << " of factor " << c->id() << " @ " << c << " is null\n";
+                        log.assertTrue((sb.get() != nullptr), inconsistency_explanation);
                     }
                 }
             }
@@ -1755,98 +1748,93 @@ bool Problem::check(bool verbose, std::ostream& stream) const
     //       MAP branch
     // ------------------------
     auto M = map_ptr_;
-    if (verbose)
-        stream << "Map @ " << M.get() << std::endl;
-    // check pointer to Problem
-    // is_consistent = is_consistent && (M->getProblem().get() == P_raw);
+    if (_verbose)
+        _stream << "Map @ " << M.get() << std::endl;
 
-    inconsistency_explanation << "The map problem ptr is " << M->getProblem().get() << " but problem is " << P_raw << "\n";
-    log.compose(CheckLog((M->getProblem().get() == P_raw), inconsistency_explanation.str()));
-    //Clear inconsistency_explanation
-    std::stringstream().swap(inconsistency_explanation);
+    // check pointer to Problem
+    inconsistency_explanation << "The map problem ptr is " << M->getProblem().get() << " but problem is " << P.get() << "\n";
+    log.assertTrue((M->getProblem() == P), inconsistency_explanation);
 
     // Landmarks =======================================================================================
     for (auto L : M->getLandmarkList())
     {
-        if (verbose)
+        if (_verbose)
         {
-            stream << "  Lmk" << L->id() << " @ " << L.get() << std::endl;
-            stream << "  -> Prb @ " << L->getProblem().get() << std::endl;
-            stream << "  -> Map @ " << L->getMap().get() << std::endl;
+            _stream << "  Lmk" << L->id() << " @ " << L.get() << std::endl;
+            _stream << "  -> Prb @ " << L->getProblem().get() << std::endl;
+            _stream << "  -> Map @ " << L->getMap().get() << std::endl;
             for (const auto& pair : L->getStateBlockMap())
             {
                 auto sb = pair.second;
-                stream <<  "  " << pair.first << " sb @ " << sb.get();
+                _stream <<  "  " << pair.first << " sb @ " << sb.get();
                 if (sb)
                 {
                     auto lp = sb->getLocalParametrization();
                     if (lp)
-                        stream <<  " (lp @ " << lp.get() << ")";
+                        _stream <<  " (lp @ " << lp.get() << ")";
                 }
-                stream << std::endl;
+                _stream << std::endl;
             }
         }
-        // check problem and map pointers
-        // is_consistent = is_consistent && (L->getProblem().get() == P_raw);
 
-        inconsistency_explanation << "The landmarks problem ptr is "
+        // check problem and map pointers
+        inconsistency_explanation << "Landmarks' problem ptr is "
                                   << L->getProblem().get() << " but problem is "
-                                  << P_raw << "\n";
-
-        log.compose(CheckLog((L->getProblem().get() == P_raw), inconsistency_explanation.str()));
-        // Clear inconsistency_explanation
-        std::stringstream().swap(inconsistency_explanation);
+                                  << P.get() << "\n";
 
-        // is_consistent = is_consistent && (L->getMap() == M);
+        log.assertTrue((L->getProblem() == P), inconsistency_explanation);
 
-        inconsistency_explanation << "The landmarks map ptr is "
+        inconsistency_explanation << "The Landmarks' map ptr is "
                                   << L->getMap() << " but map is "
                                   << M << "\n";
-        log.compose(CheckLog((M->getProblem().get() == P_raw), inconsistency_explanation.str()));
-        // Clear inconsistency_explanation
-        std::stringstream().swap(inconsistency_explanation);
-
-        for (auto cby : L->getConstrainedByList()) {
-          if (verbose)
-            stream << "      <- Fac" << cby->id() << " -> Lmk"
-                 << cby->getLandmarkOther()->id() << std::endl;
-          // check constrained_by pointer to this landmark
-          // is_consistent =
-              // is_consistent && (cby->getLandmarkOther() &&
-              //                   L->id() == cby->getLandmarkOther()->id());
-
-          inconsistency_explanation << "The landmark constrained-by loop started at "
-                                    << cby
-                                    << " is not closed\n";
-          log.compose(CheckLog((cby->getLandmarkOther() &&
-                                L->id() == cby->getLandmarkOther()->id()), inconsistency_explanation.str()));
-          // Clear inconsistency_explanation
-          std::stringstream().swap(inconsistency_explanation);
+        log.assertTrue((M->getProblem() == P), inconsistency_explanation);
+
+        for (auto cby : L->getConstrainedByList())
+        {
+          if (_verbose)
+          {
+              _stream << "      <- Fac" << cby->id() << " ->";
+
+              for (const auto& Low : cby->getLandmarkOtherList())
+              {
+                  if (!Low.expired())
+                  {
+                      const auto& Lo = Low.lock();
+                      _stream << " Lmk" << Lo->id();
+                  }
+              }
+              _stream << std::endl;
+          }
+
+          // check constrained-by factors
+          inconsistency_explanation << "constrained-by landmark " << L->id() << " @ " << L
+                                    << " not found among constrained-by factors\n";
+          log.assertTrue((cby->hasLandmarkOther(L)), inconsistency_explanation);
 
           for (auto sb : cby->getStateBlockPtrVector()) {
-            if (verbose) {
-              stream << "      sb @ " << sb.get();
+            if (_verbose) {
+              _stream << "      sb @ " << sb.get();
               if (sb) {
                 auto lp = sb->getLocalParametrization();
                 if (lp)
-                  stream << " (lp @ " << lp.get() << ")";
+                  _stream << " (lp @ " << lp.get() << ")";
               }
-              stream << std::endl;
+              _stream << std::endl;
             }
           }
         }
     }
 
-    if (verbose) stream << "--------------------------- Wolf tree " << (log.is_consistent_ ? " OK" : "Not OK !!") << std::endl;
-    if (verbose) stream << std::endl;
-    if (verbose and not log.is_consistent_) stream << log.explanation_ << std::endl;
+    if (_verbose) _stream << "--------------------------- Wolf tree " << (log.is_consistent_ ? " OK" : "Not OK !!") << std::endl;
+    if (_verbose) _stream << std::endl;
+    if (_verbose and not log.is_consistent_) _stream << log.explanation_ << std::endl;
 
     return log.is_consistent_;
 }
 
-bool Problem::check(int verbose_level) const
+bool Problem::check(int _verbose_level) const
 {
-    return check((verbose_level > 0), std::cout);
+    return check((_verbose_level > 0), std::cout);
 }
 void Problem::print(int depth, bool constr_by, bool metric, bool state_blocks) const
 {
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index d32d5c6216c857ad703c34aa1a10f4b29d6c4dc0..db82caf1fc34b83b2509fe7d4f3ac4d6cc9e8c82 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -47,13 +47,9 @@ add_library(dummy ${SRC_DUMMY})
 wolf_add_gtest(gtest_capture_base gtest_capture_base.cpp)
 target_link_libraries(gtest_capture_base ${PROJECT_NAME})
 
-# CaptureBase class test
-#wolf_add_gtest(gtest_factor_sparse gtest_factor_sparse.cpp)
-#target_link_libraries(gtest_factor_sparse ${PROJECT_NAME})
-
-# FactorBlockDifference class test
-wolf_add_gtest(gtest_factor_block_difference gtest_factor_block_difference.cpp)
-target_link_libraries(gtest_factor_block_difference ${PROJECT_NAME})
+# FactorBase class test
+wolf_add_gtest(gtest_factor_base gtest_factor_base.cpp)
+target_link_libraries(gtest_factor_base ${PROJECT_NAME})
 
 # FactorAutodiff class test
 wolf_add_gtest(gtest_factor_autodiff gtest_factor_autodiff.cpp)
@@ -169,6 +165,10 @@ target_link_libraries(gtest_factor_absolute ${PROJECT_NAME})
 wolf_add_gtest(gtest_factor_autodiff_distance_3d gtest_factor_autodiff_distance_3d.cpp)
 target_link_libraries(gtest_factor_autodiff_distance_3d ${PROJECT_NAME})
 
+# FactorBlockDifference class test
+wolf_add_gtest(gtest_factor_block_difference gtest_factor_block_difference.cpp)
+target_link_libraries(gtest_factor_block_difference ${PROJECT_NAME})
+
 # FactorOdom3d class test
 wolf_add_gtest(gtest_factor_diff_drive gtest_factor_diff_drive.cpp)
 target_link_libraries(gtest_factor_diff_drive ${PROJECT_NAME})
diff --git a/test/gtest_factor_base.cpp b/test/gtest_factor_base.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..9e4f2ef10e8bf2fc1fb9a47d48468e254e46d0af
--- /dev/null
+++ b/test/gtest_factor_base.cpp
@@ -0,0 +1,120 @@
+/*
+ * gtest_factor_base.cpp
+ *
+ *  Created on: Apr 2, 2020
+ *      Author: jsola
+ */
+
+
+#include "core/utils/utils_gtest.h"
+#include "core/utils/logging.h"
+
+#include "core/factor/factor_base.h"
+
+using namespace wolf;
+using namespace Eigen;
+
+class FactorBaseTest : public testing::Test
+{
+    public:
+        FrameBasePtr F0,F1;
+        CaptureBasePtr C0,C1;
+        FeatureBasePtr f0,f1;
+        LandmarkBasePtr L0,L1;
+
+        virtual void SetUp()
+        {
+            F0 = std::make_shared<FrameBase>(0.0, nullptr);
+            F1 = std::make_shared<FrameBase>(1.0, nullptr);
+            C0 = std::make_shared<CaptureBase>("Capture", 0.0, nullptr);
+            C1 = std::make_shared<CaptureBase>("Capture", 1.0, nullptr);
+            f0 = std::make_shared<FeatureBase>("Feature", Vector2d(1,2), Matrix2d::Identity(), FeatureBase::UncertaintyType::UNCERTAINTY_IS_COVARIANCE);
+            f1 = std::make_shared<FeatureBase>("Feature", Vector2d(1,2), Matrix2d::Identity(), FeatureBase::UncertaintyType::UNCERTAINTY_IS_COVARIANCE);
+            L0 = std::make_shared<LandmarkBase>("Lmk", nullptr);
+            L1 = std::make_shared<LandmarkBase>("Lmk", nullptr);
+        }
+//        virtual void TearDown(){}
+};
+
+class FactorDummy : public FactorBase
+{
+    public:
+        FactorDummy(const FrameBasePtr& _frame_other,
+                    const CaptureBasePtr& _capture_other,
+                    const FeatureBasePtr& _feature_other,
+                    const LandmarkBasePtr& _landmark_other) :
+                        FactorBase("Dummy",
+                                   _frame_other,
+                                   _capture_other,
+                                   _feature_other,
+                                   _landmark_other,
+                                   nullptr,
+                                   false)
+        {
+            //
+        }
+        FactorDummy(const FrameBasePtrList& _frame_other_list,
+                    const CaptureBasePtrList& _capture_other_list,
+                    const FeatureBasePtrList& _feature_other_list,
+                    const LandmarkBasePtrList& _landmark_other_list) :
+                        FactorBase("Dummy",
+                                   _frame_other_list,
+                                   _capture_other_list,
+                                   _feature_other_list,
+                                   _landmark_other_list,
+                                   nullptr,
+                                   false)
+        {
+            //
+        }
+        virtual ~FactorDummy() = default;
+
+        virtual std::string getTopology() const override {return "DUMMY";}
+        virtual bool evaluate(double const* const* _parameters, double* _residuals, double** _jacobians) const override {return true;}
+        virtual void evaluate(const std::vector<const double*>& _states_ptr, Eigen::VectorXd& _residual, std::vector<Eigen::MatrixXd>& _jacobians) const override {}
+        virtual JacobianMethod getJacobianMethod() const override {return JacobianMethod::JAC_ANALYTIC;}
+        virtual std::vector<StateBlockPtr> getStateBlockPtrVector() const override {std::vector<StateBlockPtr> v; return v;}
+        virtual std::vector<unsigned int> getStateSizes() const override {std::vector<unsigned int> v; return v;}
+        virtual unsigned int getSize() const override {return 0;}
+
+};
+
+TEST_F(FactorBaseTest, constructor_from_pointers)
+{
+    FactorDummy fac(nullptr,C0,f0,nullptr);
+
+    ASSERT_TRUE(fac.getFrameOtherList().empty());
+
+    ASSERT_EQ(fac.getCaptureOtherList().size(), 1);
+
+    ASSERT_EQ(fac.getFeatureOtherList().size(), 1);
+
+    ASSERT_TRUE(fac.getLandmarkOtherList().empty());
+}
+
+TEST_F(FactorBaseTest, constructor_from_lists)
+{
+    FactorDummy fac({},{C0},{f0,f1},{});
+
+    ASSERT_TRUE(fac.getFrameOtherList().empty());
+
+    ASSERT_EQ(fac.getCaptureOtherList().size(), 1);
+
+    ASSERT_EQ(fac.getFeatureOtherList().size(), 2);
+
+    ASSERT_TRUE(fac.getLandmarkOtherList().empty());
+}
+
+
+int main(int argc, char **argv)
+{
+    testing::InitGoogleTest(&argc, argv);
+
+    // restrict to a group of tests only
+    //::testing::GTEST_FLAG(filter) = "TestInit.*";
+
+    // restrict to this test only
+    //::testing::GTEST_FLAG(filter) = "TestInit.testName";
+
+    return RUN_ALL_TESTS();
+}
diff --git a/test/gtest_has_state_blocks.cpp b/test/gtest_has_state_blocks.cpp
index d8b46e9b721fa4f9947138eee2655ed3ad25bff0..df90859ba57d46382d97e7fa29fa66b23b137580 100644
--- a/test/gtest_has_state_blocks.cpp
+++ b/test/gtest_has_state_blocks.cpp
@@ -162,6 +162,23 @@ TEST_F(HasStateBlocksTest, Add_solve_notify_solve_add)
 
 }
 
+TEST_F(HasStateBlocksTest, hasStateBlock)
+{
+    ASSERT_TRUE(F0->hasStateBlock(sbp0));
+    ASSERT_FALSE(F0->hasStateBlock(sbv1));
+}
+
+TEST_F(HasStateBlocksTest, stateBlockKey)
+{
+    std::string key;
+    ASSERT_TRUE(F0->stateBlockKey(sbp0, key));
+    ASSERT_TRUE(key == "P");
+
+    ASSERT_FALSE(F0->stateBlockKey(sbp1, key));
+    ASSERT_TRUE(key == "");
+}
+
+
 int main(int argc, char **argv)
 {
   testing::InitGoogleTest(&argc, argv);
diff --git a/test/gtest_problem.cpp b/test/gtest_problem.cpp
index ae7e14ae893449e8c42df4736eae792dfbd4b20d..6d262ba06b81438499b29ab3d45fd4bb101c89db 100644
--- a/test/gtest_problem.cpp
+++ b/test/gtest_problem.cpp
@@ -19,8 +19,12 @@
 #include "core/sensor/sensor_diff_drive.h"
 #include "core/processor/processor_diff_drive.h"
 #include "core/capture/capture_diff_drive.h"
+//#include "core/feature/feature_diff_drive.h"
+#include "core/factor/factor_diff_drive.h"
+
 #include "core/state_block/state_quaternion.h"
 
+
 #include <iostream>
 
 using namespace wolf;
@@ -413,6 +417,70 @@ TEST(Problem, perturb)
     }
 }
 
+TEST(Problem, check)
+{
+    auto problem = Problem::create("PO", 2);
+
+    // make a sensor first
+    auto intr = std::make_shared<ParamsSensorDiffDrive>();
+    intr->radius_left                   = 1.0;
+    intr->radius_right                  = 1.0;
+    intr->wheel_separation              = 1.0;
+    intr->ticks_per_wheel_revolution    = 100;
+    Vector3d extr(0,0,0);
+    auto sensor = std::static_pointer_cast<SensorDiffDrive>(problem->installSensor("SensorDiffDrive", "sensor diff drive", extr, intr));
+    sensor->setStateBlockDynamic("I", true);
+
+    Vector3d pose; pose << 0,0,0;
+
+    int i = 0;
+    for (TimeStamp t = 0.0; t < 2.0; t += 1.0)
+    {
+        auto F = problem->emplaceFrame(KEY, pose, t);
+        if (i==0) F->fix();
+
+        for (int j = 0; j< 2 ; j++)
+        {
+            auto sb     = std::make_shared<StateBlock>(Vector3d(1,1,1));
+            auto cap    = CaptureBase::emplace<CaptureDiffDrive>(F, t, sensor, Vector2d(1,2), Matrix2d::Identity(), nullptr, nullptr, nullptr, sb);
+
+            for (int k = 0; k<2; k++)
+            {
+                Vector3d d(1,2,3), c(1,1,1);
+                Matrix3d D = Matrix3d::Identity(), J=Matrix3d::Zero();
+                auto fea = FeatureBase::emplace<FeatureMotion>(cap, "FeatureDiffDrive", d, D, c, J);
+                auto fac = FactorBase::emplace<FactorDiffDrive>(fea, fea, cap, nullptr, false);
+            }
+        }
+        i++;
+    }
+
+    for (int l = 0; l < 2; l++)
+    {
+        auto sb1    = std::make_shared<StateBlock>(Vector2d(1,2));
+        auto sb2    = std::make_shared<StateBlock>(Vector1d(3));
+        auto L      = LandmarkBase::emplace<LandmarkBase>(problem->getMap(), "LandmarkBase", sb1, sb2);
+        if (l==0) L->fix();
+    }
+
+    ASSERT_TRUE(problem->check(true, std::cout));
+
+    // remove stuff from problem, and re-check
+
+    auto F = problem->getLastKeyFrame();
+
+    auto cby = F->getConstrainedByList().front();
+
+    cby->remove(true);
+
+    ASSERT_TRUE(problem->check(true, std::cout));
+
+    F->remove();
+
+    ASSERT_TRUE(problem->check(true, std::cout));
+}
+
+
 int main(int argc, char **argv)
 {
   testing::InitGoogleTest(&argc, argv);