Publication details

Saarland University Computer Science

Unification Modulo Nonnested Recursion Schemes via Anchored Semi-Unification

Gert Smolka, Tobias Tebbi

24rd International Conference on Rewriting Techniques and Applications (RTA'13), Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik, June 2013

A recursion scheme is an orthogonal rewriting system with rules of the form f(x₁,…,xₙ) → s. We consider terms to be equivalent if they rewrite to the same redex-free possibly infinite term after infinitary rewriting. For the restriction to the nonnested case, where nested redexes are forbidden, we prove the existence of principal unifiers modulo scheme equivalence. We give an algorithm computing principal unifiers by reducing the problem to a novel fragment of semi-unification, which we call anchored semi-unification. For anchored semi-unification, we develop a decision algorithm that returns a principal semi-unifier in the positive case.

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