Hennessy-Milner Results for Probabilistic PDL

Kozen introduced probabilistic propositional dynamic logic (PPDL) in 1985 as a compositional framework to reason about probabilistic programs. In this paper we study expressiveness for PPDL and provide a series of results analogues to the classical Hennessy-Milner theorem for modal logic. First, we show that PPDL charaterises probabilistic trace equivalence of probabilistic automata (with outputs). Second, we show that PPDL can be mildly extended to yield a characterisation of probabilistic state bisimulation for PPDL models. Third, we provide a different extension of PPDL, this time characterising probabilistic event bisimulation.