A simple propositional \(\text{S}5\) tableau system
The paper presents a `remarkably simple' tableau system for the modal logic S5 and proves it soundness and weak completeness. The latter means that it captures S5-validity but not logical consequence. Using this tableau system, it is easy to understand why satisfiability in S5 is NP-complete. Also the author hopes that a similar system for first-order S5 could be constructed.
scientific article; zbMATH DE number 1308110