@InProceedings{Koz90, Author = "Kozen, D.", Year = "1990", Title = "{On Kleene Algebras and Closed Semirings}", Editor = "Rovan, B.", BookTitle = "{Proceedings of the Mathematical Foundations of Computer Science}", Place = "Banska Bystrica, Czechoslovakia", Series = "Lecture Notes in Computer Science", Number = "452", Pages = "26-47", Publisher = "Springer-Verlag", Comment = "" }