Principle of equivalence
In category theory
In category theory the principle says that properties of categories should be invariant under equivalence of categories, which has as a consequence
All grammatically correct properties of objects of a fixed category are to be invariant under isomorphism.1
Those properties which violate the principle are called evil. Thus, unless a category is univalent, it is evil to refer to equality of objects rather than isomorphism of objects.
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