Sequent Calculus Proof System Research Articles

The undecidability of proof search when equality is a logical connective

One proof-theoretic approach to equality in quantificational logic treats equality as a logical connective: in particular, term equality can be given both left and right introduction rules in a sequent calculus proof system. We present a particular example of this approach to equality in a first-order logic setting in which there are no predicate symbols (apart from equality). After we illustrate some interesting applications of this logic, we show that provability in this logic is undecidable.

Knot is not that nasty (but it is hardier than tonk)

In this paper, we evaluate Button’s claim that knot is a nasty connective. Knot’s nastiness is due to the fact that, when one extends the set $$\{ \lnot , \vee , \wedge , \rightarrow \}$$ with knot, the connective provides counterexamples to a number of classically valid operational rules in a sequent calculus proof system. We show that just as going non-transitive diminishes tonk’s nastiness, knot’s nastiness can also be reduced by dropping Reflexivity, a different structural rule. Since doing so restores all other rules in the system as validity-preserving, we are inclined to conclude that there, knot is not that nasty. However, since motivating non-reflexivity is harder than motivating non-transitivity, we also acknowledge that disagreement with our conclusion is possible.

A formal framework for specifying sequent calculus proof systems

Intuitionistic logic and intuitionistic type systems are commonly used as frameworks for the specification of natural deduction proof systems. In this paper we show how to use classical linear logic as a logical framework to specify sequent calculus proof systems and to establish some simple consequences of the specified sequent calculus proof systems. In particular, derivability of an inference rule from a set of inference rules can be decided by bounded (linear) logic programming search on the specified rules. We also present two simple and decidable conditions that guarantee that the cut rule and non-atomic initial rules can be eliminated.

On semantics of a term calculus for classical logic

The calculus of Curien and Herbelin was introduced to provide the Curry-Howard correspondence for classical logic. The terms of this calculus represent derivations in the sequent calculus proof system and reduction reflects the process of cut-elimination. We investigate some properties of two well-behaved subcalculi of untyped calculus of Curien and Herbelin, closed under the call-by-name and the call-by-value reduction, respectively. Continuation semantics is given using the category of negated domains and Moggi?s Kleisli category over predomains for the continuation monad. Soundness theorems are given for both versions thus relating operational and denotational semantics. A thorough overview of the work on continuation semantics is given.

Forum: A multiple-conclusion specification logic

The theory of cut-free sequent proofs has been used to motivate and justify the design of a number of logic programming languages. Two such languages, λProlog and its linear logic refinement, Lolli [15], provide for various forms of abstraction (modules, abstract data types, and higher-order programming) but lack primitives for concurrency. The logic programming language, LO (Linear Objects) [2] provides some primitives for concurrency but lacks abstraction mechanisms. In this paper we present Forum, a logic programming presentation of all of linear logic that modularly extends λProlog, Lolli, and LO. Forum, therefore, allows specifications to incorporate both abstractions and concurrency. To illustrate the new expressive strengths of Forum, we specify in it a sequent calculus proof system and the operational semantics of a programming language that incorporates references and concurrency. We also show that the meta theory of linear logic can be used to prove properties of the object-languages specified in Forum.

Characterizing logic grammars: A substructural logic approach

A characterization of Static Discontinuity Grammars (SDGs), a logic grammar formalism due to Dahl, is given in this paper. A substructural logic sequent calculus proof system is given which is shown to be equivalent to SDGs for parsing problems in the sense that a string of terminal symbols is accepted by a grammar if and only if the corresponding sequent is derivable in the calculus. One calculus is given for each of the two major interpretations of SDGs; the two calculi differ by only a small restriction in one rule. Since SDGs encompass other major grammar formalisms, including DCGs, the calculi serve to characterize those formalisms as well.