Let H be a subgroup of G, and let S={left cosets of H in G}, and T={Right cosets of H in G}. Now Define f: S-->T, by the following function f(aH)=H(a^-1)

Prove that f is well define!!!

All I know is "A well defined set is that if aH = bH then f(aH) = f(bH)"

Please Help!!!!