On six-valued logics of evidence and truth expanding Belnap-Dunn four-valued logic

TL;DR

This paper introduces two six-valued logics, LETK+ and LETF+, extending Belnap-Dunn four-valued logic with reliable information values, providing sound, complete semantics, and algebraic properties.

Contribution

It develops new six-valued logics with a semantics based on swap structures, extending Belnap-Dunn logic, and establishes their algebraic and proof-theoretic properties.

Findings

Defines six-valued semantics for LETK+ and LETF+

Proves algebraizability of LETK+

Shows the semantics extend Belnap-Dunn logic with reliable info

Abstract

The main aim of this paper is to introduce the logics of evidence and truth LETK+ and LETF+ together with a sound, complete, and decidable six-valued deterministic semantics for them. These logics extend the logics LETK and LETF- with rules of propagation of classicality, which are inferences that express how the classicality operator o is transmitted from less complex to more complex sentences, and vice-versa. The six-valued semantics here proposed extends the 4 values of Belnap-Dunn logic with 2 more values that intend to represent (positive and negative) reliable information. A six-valued non-deterministic semantics for LETK is obtained by means of Nmatrices based on swap structures, and the six-valued semantics for LETK+ is then obtained by imposing restrictions on the semantics of LETK. These restrictions correspond exactly to the rules of propagation of classicality that extend LETK. The logic LETF+ is obtained as the implication-free fragment of LETK+. We also show that the 6 values of LETK+ and LETF+ define a lattice structure that extends the lattice L4 defined by the Belnap-Dunn four-valued logic with the 2 additional values mentioned above, intuitively interpreted as positive and negative reliable information. Finally, we also show that LETK+ is Blok-Pigozzi algebraizable and that its implication-free fragment LETF+ coincides with the degree-preserving logic of the involutive Stone algebras.