Focusing strategies in the sequent calculus of synthetic connectives

Abstract

It is well-known that focusing striates a sequent derivation into phases of like polarity where each phase can be seen as inferring a synthetic connective. We present a sequent calculus of synthetic connectives based on neutral proof patterns, which are a syntactic normal form for such connectives. Different focusing strategies arise from different polarisations and arrangements of synthetic inference rules, which are shown to be complete by synthetic rule permutations. A simple generic cut-elimination procedure for synthetic connectives respects both the ordinary focusing and the maximally multi-focusing strategies, answering the open question of cut-admissibility for maximally multi-focused proofs. © 2008 Springer Berlin Heidelberg.