The function field is invariant under isomorphism and birational equivalence of varieties. Homeomorphism can be considered the most basic topological equivalence. Homotopy does lead to a relation on spaces&colon; homotopy equivalence. Symmetries group similar object into equivalence classes. Thus the referential transparency is limited to types without equivalence relations. Unicode provides two such notions, canonical equivalence and compatibility. Such a function is a morphism of sets equipped with an equivalence relation. It improves the rigor of certain existence and equivalence proofs. See also notions of metric space equivalence. Groupoids are generalizations of groups, group actions and equivalence relations. Logical equivalence is different from material equivalence. Sceptics of fiscal policy also make the argument of Ricardian equivalence. Let the set formula 5 have the equivalence relation formula 6. It is, as mentioned by Popper, a valid falsifier for Einstein's equivalence principle. This has an interesting consequence in terms of Morita equivalence.