Piotr Berman. Deterministic Dynamic Logic of Recursive Programs is Weaker than Dynamic Logic. In Marek Karpinski, editor, Fundamentals of Computation Theory, Proceedings of the 1983 International FCT-Conference, Borgholm, Sweden, August 21-27, 1983. Volume 158 of Lecture Notes in Computer Science, pages 14-25, Springer, 1983.