Focusing, introduced by Jean-Marc Andreoli in the context of classical linear logic, defines a normal form for sequent calculus derivations that cuts down on the number of possible derivations by eagerly applying invertible rules and grouping sequences of non-invertible rules. A focused sequent calculus is defined relative to some non-focused sequent calculus; focalization is the property that ...

In this paper we explore a generalization of traditional abduction which can simultaneously perform two different tasks: (i) given an unprovable sequent G, find a sentence H such that ,H G is provable (hypothesis generation); (ii) given a provable sequent G, find a sentence H such that H and the proof of ,H G is simpler than the proof of G (lemma generation). We argue that the two tasks should ...

Bi-intuitionistic logic is the conservative extension of intuitionistic logic with a connective dual to implication. It is sometimes presented as a symmetric constructive subsystem of classical logic. In this talk, we compare three sequent calculi for bi-intuitionistic propositional logic: (1) a basic standard-style sequent calculus that restricts the premises of implication-right and exclusion...

Classical logic and more precisely classical sequent calculi are currently the subject of several studies that aim at providing them with an algorithmic meaning. They are however ruled by an annoying syntactic bureaucracy which is a cause of pathologic non-confluence. An interesting patch consists in representing proofs using proofnets. This leads (at least in the propositional case) to cut-eli...

Sufficient conditions for first order based sequent calculi to admit cut elimination by a Schütte-Tait style cut elimination proof are established. The worst case complexity of the cut elimination is analysed. The obtained upper bound is parameterized by a quantity related with the calculus. The conditions are general enough to be satisfied by a wide class of sequent calculi encompassing, among...

Gentzen’s Hauptsatz – cut elimination theorem – in sequent calculi reveals a fundamental property on logic connectives in various logics such as classical logic and intuitionistic logic. In this paper, we implement a procedure in Haskell to perform cut elimination for intuitionistic sequent calculus, where we use types to guarantee that the procedure can only return a cut-free proof of the same...

Several deductive formalisms (e.g., sequent, nested sequent, labeled sequent, hypersequent calculi) have been used in the literature for the treatment of modal logics, and some connections between these formalisms are already known. Here we propose a general framework, which is based on a focused version of the labeled sequent calculus by Negri, augmented with some parametric devices allowing t...

What is the semantics of Negation-as-Failure in logic programming? We try to answer this question by proof-theoretic methods. A rule based sequent calculus is used in which a sequent is provable if, and only if, it is true in all three-valued models of the completion of a logic program. The main theorem is that proofs in the sequent calculus can be transformed into SLDNF-computations if, and on...