In a total one-to-one mapping from concepts to extensions, the cardinality of extensions is at least as large as the cardinality of concepts.

So the contrapositive asserts that if \(\neg \forall x(Fx \equiv Gx)\) then \(\epsilon F \neq \epsilon G\). But in the case where the material equivalence of \(F\) and \(G\) is a sufficient condition for \(F = G\), i.e., in the case where \(F \neq G\) implies \(\neg \forall x(Fx \equiv Gx)\), then Vb implies \(F \neq G \to \epsilon F \neq \epsilon G\), i.e., that if concepts \(F\) and \(G\) differ, the extensions of \(F\) and \(G\) differ. So, the correlation that Basic Law V sets up between co