Hybrid Logic and its Proof-Theory

This book is the first book-length treatment of hybrid logic and its proof-theory. Hybrid logic is an extension of ordinary modal logic which allows explicit reference to individual points in a model. The extra expressive power is useful for many applications, for example, when reasoning about time one often wants to formulate a series of statements about what happens at specific times.§There is little consensus about proof-theory for ordinary modal logic. Many modal-logical proof systems lack important properties and the relationships between proof systems for different modal logics are often unclear. The present book demonstrates that hybrid-logical proof-theory remedies this lack of uniformity in ordinary modal-logical proof systems. It considers a spectrum of different versions of hybrid logic (propositional, first-order, international first-order, and intuitionist) and of different types of proof-systems for hybrid-logic (natural deduction, Gentzen, tableaux, and axiom systems). All these systems can be motivated independently, but the fact that the systems can be given in a uniform way shows that hybrid logic and hybrid-logical proof theory is a natural enterprise.