Aggressive simplification: apply substitutions from shared conclusions.
Bug fix in `equal` example.
Pass as parameters to unification all `bs` variables in abduction. Debugging output turned on. Recover error information when abduction fails.
Handle Not_in_scope in the same way as Same_quant. More stringent validate in abduction (with both premise and conclusion of each branch). More thorough backtracking in abduction for terms. Temporary debug logging.
Simplify by eliminating shared conclusions: do not substitute predicate variable arguments; make optional. Invariants: bug fix in variable comparison. Test suite cleanup.