* Simplify adding lemmas
* Remove misleading constructor from tmp_assign.
The idea is that tmp_assign is only created on the stack and
short-lived. Instead of having a convenience constructor that takes a
constraint_ref, it's clearer to have an explicit .get() at the call
site.
* Remove some log messages
* bugfix
* fix
* Add stub for conflict_core
* wip
* Add example by Clemens
