Proof that Let G G 1 X X G n For each i let i G i G be the inclusion map and i G G i the canonical projection (see page 59) Let i , i i , Then the sum i1 'P ik of any k (1 k n) distinct i , is a normal endomorphism of G ...

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Proof that Let G = G 1 X X G n . For each

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Proof that Let G = G₁ X · · · X G_n. For each i let λ_i: G_i → G be the inclusion map and π_i : G → G_i the canonical projection (see page 59). Let φ_i,= λ_iπ_i,. Then the "sum" φ_i1 + · · · + 'P_ik of any k (1 ≤ k ≤ n) distinct φ_i , is a normal endomorphism of G.