Powering-invariant not implies divisibility-closed
This article gives the statement and possibly, proof, of a non-implication relation between two subgroup properties. That is, it states that every subgroup satisfying the first subgroup property (i.e., powering-invariant subgroup) need not satisfy the second subgroup property (i.e., divisibility-invariant subgroup)
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Statement
It is possible to have a group and a subgroup
Proof
Proof idea
The key fact is that any finite subgroup of a group must be powering-invariant, but it need not be divisibility-invariant. We will construct an example where the subgroup is finite.
Proof details
For any prime number , let be the -quasicyclic group. Let be the subgroup comprising the elements of order 1 or . Clearly, , being finite, is powering-invariant (in fact, both and are powered over precisely the set of primes other than ). However, is not divisibility-invariant: is -divisible, but is not.