Decision Problems for Term Rewrite Systems and Recognizable Tree Languages
Abstract
We study the connections between recognizable tree languages and rewrite systems. We investigate some decision problems. Particularly, let us consider the property (P): a rewrite system S is such that, for every recognizable tree language F, the set of S-normal forms of terms in F is recognizable too. We prove that the property (P) is undecidable. We prove that the existential fragment of the theory of ground term algebras modulo a congruence $$\mathop \leftrightarrow \limits^* E$$ generated by a set E of equations such that there exists a finite, noetherian, confluent rewrite system S satisfying (P) with $$\mathop \leftrightarrow \limits^* S = \mathop \leftrightarrow \limits^* E$$ is undecidable. Nevertheless, we develop a decision procedure for the validity of linear formulas in a fragment of such a theory.