Model-checking an Epistemic \mu-calculus with Synchronous and Perfect   Recall Semantics
  We show that the model-checking problem is decidable for a fragment of the epistemic \mu-calculus. The fragment allows free variables within the scope of epistemic modalities in a restricted form that avoids constructing formulas embodying any form of common knowledge. Our calculus subsumes known decidable fragments of epistemic CTL/LTL. Its modal variant can express winning strategies in two-player games with one player having imperfect information and non-observable objectives, and, with a suitable encoding, decidable instances of the model-checking problem for ATL with imperfect information and perfect recall can be encoded as instances of the model-checking problem for this epistemic \mu-calculus. 
Rodica Bozianu and C\u{a}t\u{a}lin Dima and Constantin Enea
cs.LO