Claudia Pons Maximo Prieto Luis Olsina A Formal Mechanism for Assessing Polymorphism in Object-Oriented Systems. 53-62 2000 conf/apaqs/2000 APAQS http://doi.ieeecomputersociety.org/10.1109/APAQ.2000.883778 db/conf/apaqs/apaqs2000.html#PonsPO00