Va only entails that distinct extensions are correlated with distinct concepts, which is a functional constraint on concept-to-extension mapping.

So the contrapositive asserts that if \(\epsilon F \neq \epsilon G\), then \(\neg \forall x(Fx \equiv Gx)\). But in the case where the material equivalence of \(F\) and \(G\) is a necessary condition for \(F = G\), i.e., in the case where \(\neg \forall x(Fx \equiv Gx)\) implies \(F \neq G\), then Va implies that if \(\epsilon F \neq \epsilon G\), then \(F \neq G\), i.e., that whenever the extensions of \(F\) and \(G\) differ, the concepts with which they are correlated, namely \(F\) and \(G\),