 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 concepts and extensions will have to be one-to-one; i.e., it correlates distinct concepts with distinct extensions. Since every concept is correlated with some extension, there have to be at least as many extensions as there are concepts.