Recall that if f : A → B is a one-to-one function mapping A onto B, then f^-1 (b) is the unique a ∈ A such that f(a) = b. Prove that if ∅: S-+ S' is an isomorphism of (S, *) with (S', *'), then ∅^-1 is an isomorphism of
(S', *') with (S, *).