Strategies for combining decision procedures

  • Authors:

  • Sylvain Conchon;Sava Krstic

  • Affiliations:

  • École des Mines de Nantes;OGI School of Science & Engineering at Oregon Health & Sciences University

  • Venue:
  • TACAS'03 Proceedings of the 9th international conference on Tools and algorithms for the construction and analysis of systems
  • Year:
  • 2003

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Abstract

Implementing efficient algorithms for combining decision procedures has been a challenge and their correctness precarious. In this paper we describe an inference system that has the classical Nelson-Oppen procedure at its core and includes several optimizations: variable abstraction with sharing, canonization of terms at the theory level, and Shostak's streamlined generation of new equalities for theories with solvers. The transitions of our system are fine-grained enough to model most of the mechanisms currently used in designing combination procedures. In particular, with a simple language of regular expressions we are able to describe several combination algorithms as strategies for our inference system, from the basic Nelson-Oppen to the very highly optimized one recently given by Shankar and Rueß. Presenting the basic system at a high level of generality and nondeterminism allows transparent correctness proofs that can be extended in a modular fashion whenever a new feature is introduced in the system. Similarly, the correctness proof of any new strategy requires only minimal additional proof effort.