Ondrej Klíma, Libor Polák. Hierarchies of Piecewise Testable Languages. In Masami Ito, Masafumi Toyama, editors, Developments in Language Theory, 12th International Conference, DLT 2008, Kyoto, Japan, September 16-19, 2008. Proceedings. Volume 5257 of Lecture Notes in Computer Science, pages 479-490, Springer, 2008. [doi]
Abstract is missing.