Ralph-Johan Back Anna Mikhajlova Joakim von Wright Class Refinement as Semantics of Correct Object Substitutability. 18-40 2000 12 Formal Asp. Comput. 1 http://link.springer.de/link/service/journals/00165/bibs/0012001/00120018.htm db/journals/fac/fac12.html#BackMW00