Meeting strength in substructural logics

This paper contributes to the theory of hybrid substructural logics, i.e. weak logics given by a Gentzen-style proof theory in which there is only a limited possibility to use structural rules. Following the literature, we use an operator to mark formulas to which the extra structural rules may be applied. New in our approach is that we do not see this ∇ as a modality, but rather as the meet of the marked formula with a special type Q. In this way we can make the specific structural behaviour of marked formulas more explicit. The main motivation for our approach is that we can provide a nice, intuitive semantics for hybrid substructural logics. Soundness and completeness for this semantics are proved; besides this we consider some proof-theoretical aspects like cut-elimination and embeddings of the ‘strong’ system in the hybrid one. ∗Faculteit Wiskunde en Informatica, Vrije Universiteit, Amsterdam & Centrum voor Wiskunde en Informatica, P.O. Box 4079, 1009 GB Amsterdam; e-mail: [email protected]