The Logic for Mathematics without Ex Falso Quodlibet

Abstract

Abstract Informally rigorous mathematical reasoning is relevant. So too should be the premises to the conclusions of formal proofs that regiment it. The rule Ex Falso Quodlibet induces spectacular irrelevance. We therefore drop it. The resulting systems of Core Logic C and Classical Core Logic C+ can formalize all the informally rigorous reasoning in constructive and classical mathematics respectively. We effect a revised match-up between deducibility in Classical Core Logic and a new notion of relevant logical consequence. It matches better the deducibility relation of Classical Core Logic than does the Tarskian notion of consequence. It is implosive, not explosive.