function getTop()

Created by: joansola

Is it really necessary? Can we rename it to getProblem()? Then we can simplify some things:

• location_ in NodeLinked not necessary
• location_ in WolfProblem not necessary

Created by: joansola

I think if this is really needed we should overload it with a more efficient implementation. But the issue here, by now, is renaming it.

Created by: joanvallve

I would fuse this issue with the nodeLinked elimination

mentioned in commit 2ead95a3