Model Checking Games for Branching Time Logics

This paper defines and examines model checking games for the branching time temporal logic CTL∗. The games employ a technique called focus which enriches sets by picking out one distinguished element. This is necessary to avoid ambiguities in the regeneration of temporal operators. The correctness of these games is proved, and optimisations are considered to obtain model checking games for important fragments of CTL∗. A game based model checking algorithm that matches the known lower and upper complexity bounds is sketched.