Philippe Collet Alain Ozanne Nicolas Rivierre Towards a Versatile Contract Model to Organize Behavioral Specifications. 844-855 2007 conf/sofsem/2007 SOFSEM (1) http://dx.doi.org/10.1007/978-3-540-69507-3_73 db/conf/sofsem/sofsem2007.html#ColletOR07