Abstract Partial Cylindrical Algebraic Decomposition I: The Lifting Phase

Partial Cylindrical Algebraic Decomposition I: The Lifting Phase Grant Olney Passmore and Paul B. Jackson [email protected], [email protected] 1 Clare Hall, University of Cambridge 2 LFCS, University of Edinburgh Abstract. Though decidable, the theory of real closed fields (RCF) is Though decidable, the theory of real closed fields (RCF) is fundamentally infeasible. This is unfortunate, as automatic proof methods for nonlinear real arithmetic are crucially needed in both formalised mathematics and the verification of real-world cyber-physical systems. Consequently, many researchers have proposed fast, sound but incomplete RCF proof procedures which are useful in various practical applications. We show how such practically useful, sound but incomplete RCF proof methods may be systematically utilised in the context of a complete RCF proof method without sacrificing its completeness. In particular, we present an extension of the RCF quantifier elimination method Partial CAD (P-CAD) which uses incomplete ∃ RCF proof procedures to “short-circuit” expensive computations during the lifting phase of PCAD. We present the theoretical framework and preliminary experiments arising from an implementation in our RCF proof tool RAHD.