Dietmar Berwanger, Giacomo Lenzi. The Variable Hierarchy of the µ-Calculus Is Strict. In Volker Diekert, Bruno Durand, editors, STACS 2005, 22nd Annual Symposium on Theoretical Aspects of Computer Science, Stuttgart, Germany, February 24-26, 2005, Proceedings. Volume 3404 of Lecture Notes in Computer Science, pages 97-109, Springer, 2005. [doi]
Abstract is missing.