olemus
ISO/IEC/IEEE24765:
kahe objekti selline identne kätumine, et üks objekt saab asendada teist mingite kriteeriumide põhjal, mille korral keskkond ei märka objektide käitumise erinevust
= identical behavior of two objects, such that one object can replace the other with respect to a set of criteria without the environment being able to notice the difference in the objects' behavior on the basis of the set of criteria