P. Godefroid. CAV (DIMACS/AMS volume), volume 3 of DIMACS Series in Discrete Mathematics and Theoretical Computer Science, page 321-340. DIMACS/AMS, (1990)
P. Godefroid, and P. Wolper. CAV '91: Proceedings of the 3rd International Workshop on Computer Aided Verification, page 332--342. London, UK, Springer-Verlag, (1992)