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 signiicantly extend the safe unfold/fold transformation sequence presented in 11]. By exploiting typing information, more useful conditions can be deened 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 rst step in the direction of exploiting a Pre/Post speciication on the intended use of the program to be transformed. Such speciication can restrict the instances of queries and clauses to be considered and then relax the applicability conditions on the transformation operations.