Hint Orchestration Using ACL2's Simplifier

TL;DR

This paper introduces a hint orchestration strategy for ACL2 proofs using the use-termhint utility, enabling more flexible and robust hint management during proof simplification.

Contribution

It presents a novel method for providing case-specific hints and variable bindings that are resilient to rewriting changes in ACL2 proofs.

Findings

Supports case split hints with different cases

Allows variable binding to avoid repeated subterms

Enhances robustness against rewriting variations

Abstract

This paper describes a strategy for providing hints during an ACL2 proof, implemented in a utility called use-termhint. An extra literal is added to the goal clause and simplified along with the rest of the goal until it is stable under simplification, after which the simplified literal is examined and a hint extracted from it. This simple technique supports some commonly desirable yet elusive features. It supports providing different hints to different cases of a case split, as well as binding variables so as to avoid repeating multiply referenced subterms. Since terms used in these hints are simplified in the same way as the rest of the goal, this strategy is also more robust against changes in the rewriting normal form than hints in which terms from the goal are written out explicitly.