Normal forms and functional completeness for four-valued languages

Abstract

Based on the semantic concepts developed by M.~Dunn and N.~Belnap, a four-valued language containing only two logical symbols is proposed. We show that this language is functionally complete with regard to the given semantics. Specifically, we prove that every truth-function is expressed by a formula of the language. To do this, we define two concepts akin to the disjunctive and conjunctive normal forms. Using these concepts, we establish that every truth-function for a four-valued semantics can be represented by a formula in a disjunctive form or in a conjunctive form.