Primitive Rewriting

Undecidability results in rewriting have usually been proved by reduction from undecidable problems of Turing machines or, more recently, from Post’s Correspondence Problem. Another natural candidate for proofs regarding term rewriting is Recursion Theory, a direction we promote in this contribution. We present some undecidability results for “primitive” term rewriting systems, which encode primitive-recursive definitions, in the manner suggested by Klop. We also reprove some undecidability results for orthogonal and non-orthogonal rewriting by applying standard results in recursion theory.