 Vopenka considers representations of superclasses of classes using relations on sets. A class relation \(R\) on a class \(A\) is said to code the superclass of inverse images of elements of \(A\) under \(R\). A class relation \(R\) on a class \(A\) is said to extensionally code this superclass if distinct elements of \(A\) have distinct preimages. He “tidies up” the theory of such codings by adopting the