Complemented normal implies endomorphism kernel
This article gives the statement and possibly, proof, of an implication relation between two subgroup properties. That is, it states that every subgroup satisfying the first subgroup property (i.e., complemented normal subgroup) must also satisfy the second subgroup property (i.e., endomorphism kernel)
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The proof is direct: the subgroup isomorphic to the quotient group is simply the permutable complement to the normal subgroup. This follows from Fact (1).
The endomorphism in question is the retraction onto that complement, i.e., the map that sends every element of the group to the unique element of the complement in its coset with respect to the normal subgroup.