Partial Automata and Finitely Generated Congruences: An Extension of Nerode's Theorem

Abstract

Let T_Sigma be the set of ground terms over a finite ranked alphabet Sigma. We define partial autornata on T_Sigma and prove that the finitely generated congruences on T_Sigma are in one-to one correspondence (up to isomorphism) with the finite partial automata on Sigma with no inaccessible and no inessential states. We give an application in term rewriting: every ground term rewrite system has a canonical equivalent system that can be constructed in polynomial time.