Replacement Can Preserve Termination

We consider the replacement transformation operation, a very general and powerful transformation, and study under which conditions it preserves universal termination besides computed answer substitutions. With this safe replacement we can significantly extend the safe unfold/fold transformation sequence presented in [11]. By exploiting typing information, more useful conditions can be defined and we may deal with some special cases of replacement very common in practice, namely switching two atoms in the body of a clause and the associativity of a predicate. This is a first step in the direction of exploiting a Pre/Post specification on the intended use of the program to be transformed. Such specification can restrict the instances of queries and clauses to be considered and then relax the applicability conditions on the transformation operations.

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