Pattern-based Subterm Selection in Isabelle

This article presents a pattern-based language designed to select (a set of) subterms of a given term in a concise and robust way. Building on this language, we implement a single-step rewriting tactic in the Isabelle theorem prover, which removes the need for obscure "occurrence numbers" for subterm selection. The language was inspired by the \emph{language of patterns} of Gonthier and Tassi, but provides an elegant way of handling bound variables and a modular semantics.