Abelian direct factor implies potentially verbal in finite

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This article gives the statement and possibly, proof, of an implication relation between two subgroup properties, when the big group is a finite group. That is, it states that in a Finite group (?), every subgroup satisfying the first subgroup property (i.e., Abelian direct factor (?)) must also satisfy the second subgroup property (i.e., Potentially verbal subgroup (?)). In other words, every Abelian direct factor of finite group is a potentially verbal subgroup of finite group.
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Statement

Suppose G is a finite group and H is a direct factor of G such that H is Abelian as a group. Then, there exists a group K containing G such that H is a verbal subgroup.

Facts used

  1. structure theorem for finitely generated Abelian groups

Proof

Given: A finite group G with direct factor H. Let L be a normal complement to H in G, so GH×L.

To prove: There exists a group K containing G such that H is a verbal subgroup of K.

Proof: If H is trivial, we can set K=G and be done. So, we can assume H is nontrivial.

  1. By fact (1), we can write H as a direct product of cyclic groups, say H=C1×C2××Cr, where each Ci is cyclic of prime power order, say piki.
  2. For each prime p, let c(p) be a positive integer greater than the largest power of p dividing the order of L. (Note that the same p may repeat among multiple pis).
  3. Now consider the group M=D1×D2××Dr where each Di is cyclic of order piki+c(pi). Treat H as the subgroup of M obtained by embedding each Ci naturally into the corresponding Di.
  4. Define K=M×L, with G embedded in K using the embedding of H in M provided above.
  5. Let n=pc(p) where the product is over the primes p dividing the order of H. Then, it is clear that the set of nth powers in K is precisely H. In particular, H is a verbal subgroup of K.