A Fibred Tableau Calculus for Modal Logics of Agents

In [15,19] we showed how to combine propositional multimodal logics using Gabbay’s fibring methodology. In this paper we extend the above mentioned works by providing a tableau-based proof technique for the combined/fibred logics. To achieve this end we first make a comparison between two types of tableau proof systems, (graph & path), with the help of a scenario (The Friend’s Puzzle). Having done that we show how to uniformly construct a tableau calculus for the combined logic using Governatori’s labelled tableau system KEM. We conclude with a discussion on KEM’s features.