Comparing Levels of Bisimulation Quantifiers Logic with the mu-calculus Giovanna D'Agostino, Giacomo Lenzi Abstract: In this paper we deal with the logic of Bisimulation Quantifiers BQL. This is a logic extending PDL by means of bisimulation quantifiers: an existential bisimulation quantifier acts like a standard existential set quantifier but allows to look for a set not only within the model, but in any other model which is bisimilar to the given one. It is known that BQL has the same expressive power than the mu-calculus. In this paper we give a finer look to this correspondence, by defining a hierarchy for BQL and comparing it with the mu-calculus hierarchy. Keywords: Bisimulation Quantifiers, mu-calculus, hierarchy problems