(1991 -). VDM'91 Formal Software Development Methods. 4th International Symposium of VDM Europe Noordwijkerhout,Th. Berlin: Springer- Verlag,.
VDM'91 Formal Software Development Methods: 4th International Symposium of VDM Europe Noordwijkerhout,Th. Berlin: Springer- Verlag; 1991 -. ISBN: 3-540-54834-3.