David A. Penny Richard C. Holt Michael W. Godfrey Formal Specification in Metamorphic Programing. 11-30 1991 conf/fm/1991-1 VDM Europe (1) db/conf/fm/vdme1991-1.html#PennyHG91 http://dx.doi.org/10.1007/3-540-54834-3_4