Fix comment

include/core/factor/factor_quaternion_absolute.h

@@ -72,7 +72,7 @@ inline bool FactorQuaternionAbsolute::operator ()(const T* const _o, T* _residua
      *
      * In rotations.h, we have
      *      minus(q1,q2) = minus_right(q1,q2) = log_q(q1.conjugate() * q2); --> this is a local 'minus'
-     *      minus_left(q1,q2) = log_q(q2.conjugate() * q1); --> this is a global 'minus'
+     *      minus_left(q1,q2) = log_q(q2 * q1.conjugate()); --> this is a global 'minus'
      */ 
 
     Eigen::Matrix<T, 3, 1> er;