Justifying Equality

We consider the problem of finding irredundant bases for inconsistent sets of equalities and disequalities. These are subsets of inconsistent sets which do not contain any literals which do not contribute to the unsatisfiability in an essential way, and can therefore be discarded. The approach we are pursuing here is to decorate derivations with proofs and to extract irredundant sets of assumptions from these proofs. This requires specialized operators on proofs, but the basic inference systems are otherwise left unchanged. In particular, we include justifying inference systems for union-find structures and abstract congruence closure, but our constructions can also be applied to other inference systems such as Gaussian elimination.