VDM ʹ90. VDM and Z-Formal methods in software development : Third international symposium of VDM Europe Kiel, FRG, April 1990: Proceedings ; D. Bjorner, C. A. R. Hoare, H. Langmaack - Bjorner, D.; Hoare, C.A.R.; Langmaack, Hans (Lecture notes in computer science,, 1990)