Generalize relations between locations in the invariant. #71
Description
Currently, SSProve provides a few specific SemiInvariants such as couple_rhs, couple_lhs and triple_rhs. However, a custom definition is needed if one wants to couple a lhs locations to a rhs location.
Some code already generalized this, but it was removed as part of #65 and it is unclear how well it worked as it was not used in any of the examples.
The code is found here: