Endomorphism image implies divisibility-closed
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., endomorphism image) must also satisfy the second subgroup property (i.e., divisibility-closed subgroup)
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Statement
Suppose is a group and is a subgroup of that is an endomorphism image of , i.e., there exists an endomorphism of such that . Then, is a divisibility-closed subgroup of , i.e., if is a natural number such that every element of has a root (not necessarily unique) in , then every element of has a root (not necessarily unique) in .
Facts used
Proof
Proof idea
The proof idea is to take an inverse image under the endomorphism, take the root, and then take the image again. More abstractly, we can simply use Fact (1).