Compact Normalisation Trace via Lazy Rewriting

Abstract

Innermost strategies are usually used in compiling term rewriting systems (TRSs) since they allow to efficiently build result terms in a bottom-up fashion. However, innermost strategies do not always give the shortest normalising derivation. In many cases, using an appropriate laziness annotation on the arguments of function symbols, we evaluate lazy arguments only if it is necessary and hence, get a shorter derivation to normal forms while avoiding non-terminating reductions. We provide in this work a transformation of annotated TRSs, that allows to compute normal forms using an innermost strategy and to extract lazy derivations in the original TRS from normalising derivations in the transformed TRS. We apply our result to improve the efficiency of equational reasoning in Coq proof assistant using ELAN as an external rewriting engine.