George Metcalfe

Fuzzy logics based on [0,1)-continuous uninorms

Axiomatizations are presented for fuzzy logics characterized by uninorms continuous on the half-open real unit interval [0,1), generalizing the continuous t-norm based approach of Hájek. Basic uninorm logic BUL is defined and completeness is established with respect to algebras with lattice reduct [0,1] whose monoid operations are uninorms continuous on [0,1). Several extensions of BUL are also introduced. In particular, Cross ratio logic CRL, is shown to be complete with respect to one special uninorm. A Gentzen-style hypersequent calculus is provided for CRL and used to establish co-NP completeness results for these logics.

Sequent and hypersequent calculi for abelian and łukasiewicz logics

We present two embeddings of Łukasiewicz logic <b>Ł</b> into Meyer and Slaneys Abelian logic <b>A</b>, the logic of lattice-ordered Abelian groups. We give new analytic proof systems for <b>A</b> and use the embeddings to derive corresponding systems for <b>Ł</b>. These include hypersequent calculi, terminating hypersequent calculi, co-NP labeled sequent calculi, and unlabeled sequent calculi.

Proof theory for admissible rules

Admissible rules of a logic are those rules under which the set of theorems of the logic is closed. In this paper, a Gentzen-style framework is introduced for analytic proof systems that derive admissible rules of non-classical logics. While Gentzen systems for derivability treat sequents as basic objects, for admissibility, the basic objects are sequent rules. Proof systems are defined here for admissible rules of classes of modal logics, including K4, S4, and GL, and also Intuitionistic Logic IPC. With minor restrictions, proof search in these systems terminates, giving decision procedures for admissibility in the logics.

Uniform Rules and Dialogue Games for Fuzzy Logics

We provide uniform and invertible logical rules in a framework of relational hypersequents for the three fundamental t-norm based fuzzy logics i.e., Łukasiewicz logic, Godel logic, and Product logic. Relational hypersequents generalize both hypersequents and sequents-of-relations. Such a framework can be interpreted via a particular class of dialogue games combined with bets, where the rules reflect possible moves in the game. The problem of determining the validity of atomic relational hypersequents is shown to be polynomial for each logic, allowing us to develop Co-NP calculi. We also present calculi with very simple initial relational hypersequents that vary only in the structural rules for the logics.

Admissible rules in the implication–negation fragment of intuitionistic logic

Abstract Uniform infinite bases are defined for the single-conclusion and multiple-conclusion admissible rules of the implication–negation fragments of intuitionistic logic IPC and its consistent axiomatic extensions (intermediate logics). A Kripke semantics characterization is given for the (hereditarily) structurally complete implication–negation fragments of intermediate logics, and it is shown that the admissible rules of this fragment of IPC form a PSPACE-complete set and have no finite basis.

Structural Completeness in Fuzzy Logics

Structural completeness properties are investigated for a range of popular t-norm based fuzzy logics—including Łukasiewicz Logic, Gödel Logic, Product Logic, and Hájek’s Basic Logic—and their fragments. General methods are defined and used to establish these properties or exhibit their failure, solving a number of open problems.

Hypersequent Systems for the Admissible Rules of Modal and Intermediate Logics

The admissible rules of a logic are those rules under which the set of theorems of the logic is closed. In a previous paper by the authors, formal systems for deriving the admissible rules of Intuitionistic Logic and a class of modal logics were defined in a proof-theoretic framework where the basic objects of the systems are sequent rules. Here, the framework is extended to cover derivability of the admissible rules of intermediate logics and a wider class of modal logics, in this case, by taking hypersequent rules as the basic objects.

Density elimination

Density elimination, a close relative of cut elimination, consists of removing applications of the Takeuti-Titani density rule from derivations in Gentzen-style (hypersequent) calculi. Its most important use is as a crucial step in establishing standard completeness for syntactic presentations of fuzzy logics; that is, completeness with respect to algebras based on the real unit interval [0,1]. This paper introduces the method of density elimination by substitutions. For general classes of (first-order) hypersequent calculi, it is shown that density elimination by substitutions is guaranteed by known sufficient conditions for cut elimination. These results provide the basis for uniform characterizations of calculi complete with respect to densely and linearly ordered algebras. Standard completeness follows for many first-order fuzzy logics using a Dedekind-MacNeille-style completion and embedding.

Analytic Calculi for Product Logics

Abstract.Product logic Π is an important t-norm based fuzzy logic with conjunction interpreted as multiplication on the real unit interval [0,1], while Cancellative hoop logic CHL is a related logic with connectives interpreted as for Π but on the real unit interval with 0 removed (0,1]. Here we present several analytic proof systems for Π and CHL, including hypersequent calculi, co-NP labelled calculi and sequent calculi.

Proof Systems for a Gödel Modal Logic

A basic propositional modal fuzzy logic