In: Advanced Math
Let φ : G1 → G2 be a group homomorphism. (abstract algebra)
(a) Suppose H is a subgroup of G1. Define φ(H) = {φ(h) | h ∈ H}. Prove that φ(H) is a subgroup of G2.
(b) Let ker(φ) = {g ∈ G1 | φ(g) = e2}. Prove that ker(φ) is a subgroup of G1.
(c) Prove that φ is a group isomorphism if and only if ker(φ) = {e1} and φ(G1) = G2.