Henzinger, Thomas A., et al. “On the Universal and Existential Fragments of the Mu-Calculus.”10.1007/3-540-36577-X_5__Proceedings of the 9th International Conference on Tools and Algorithms for the Construction and Analysis of Systems , vol. 2619, Springer, 2003, pp. 49–64, doi:10.1007/3-540-36577-X_5.