Semantic Path Orders are Generalized Weighted Path Orders

Abstract

Monotonic semantic path orders (MSPOs) are powerful reduction orders, but their effective use in theorem proving and termination analysis raises three issues: efficient comparison of terms, ground totality, and a reduction-pair formulation. Inspired by weighted path orders (WPOs), we introduce generalized weighted path orders (GWPOs) which encompass both WPOs and MSPOs. GWPOs and MSPOs coincide as classes of reduction orders, thereby yielding efficient and ground-total subclasses of MSPOs. We further formulate the reduction-pair version of the GWPO for the dependency pair method, from which a reduction-pair version of the MSPO is obtained. In contrast to the reduction-order setting, the correspondence between GWPOs and MSPOs no longer fully carries over, establishing the GWPO as a framework of independent interest. Effectiveness of the resulting reduction pairs is assessed by standard termination benchmarks.