Abelian-quotient not implies kernel of a bihomomorphism

From Groupprops

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., abelian-quotient subgroup) need not satisfy the second subgroup property (i.e., kernel of a bihomomorphism)
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Statement

There are three different but equivalent formulations (in the sense that any example for one formulation also furnishes examples for the other):

  1. It is possible to have an abelian group such that there is no bihomomorphism to any group with kernel the trivial subgroup of .
  2. It is possible to have a group and an abelian-quotient subgroup of such that there is no bihomomorphism for any group with kernel .
  3. It is possible to have a nilpotent group such that there is no bihomomorphism to any group with kernel the [[derived subgroup] of .

Facts used

  1. Kernel of a bihomomorphism implies completely divisibility-closed

Proof

We will furnish an example for (1), which also gives examples for (2) and (3).

Let be a prime number. Let be the quasicyclic group for , i.e., the group of all roots of unity for all . is an abelian group.

The trivial subgroup is not completely divisibility-closed in : is -divisible but the identity element has roots outside the trivial subgroup.