1. Carrillo-Castellon, M., Garcia-Molina, J., Pimentel, E., Repiso, I.: Design by contract in Smalltalk. Journal of Object-Oriented Programming 7(9), 23–28 (1996)
2. Lecture Notes in Computer Science;O. Chitil,2007
3. Chitil, O., Huch, F.: Monadic prompt lazy assertions in Haskell. In: Asian Symposium on Programming Languages and Systems (2007)
4. Lecture Notes in Computer Science;O. Chitil,2004
5. Conway, D., Goebel, C.G.: Class: Contract – design-by-contract OO in Perl,
http://search.cpan.org/~ggoebel/Class-Contract-1.14/