A Sound and Complete Axiomatisation for Intuitionistic Linear Temporal Logic

Intuitionistic linear temporal logic (iLTL) has been studied extensively, especially in the last decade. It enjoys natural semantics over intuitionistic Kripke frames equipped with an order-preserving function representing the temporal dynamics, known as 'expanding models'. This leads to a logic that is known to be decidable but whose axiomatisation has long remained open. We propose an extension of iLTL with the co-implication connective of Hilbert–Brouwer logic and call it 'bi-intuitionistic linear temporal logic' (biLTL). We establish that this extension is still decidable for the class of expanding models. We moreover give a sound and complete Hilbert-style calculus for it, the first for any logic extending iLTL. As a corollary, the topological semantics for intuitionistic propositional logic cannot be extended to a topological semantics for Hilbert-Brouwer logic, which thus establishes co-implication as a distinctive feature of the Kripke semantics for bi-intuitionistic logic.