On finite groups in which the twisted conjugacy classes of the unit element are subgroups

Abstract

We consider groups $G$ such that the set $[G,\phi ]=\{g^{-1}{g}^{\phi }|g\in G\}$ is a subgroup for every automorphism $\phi$ of $G$, and we prove that there exists such a group $G$ that is finite and nilpotent of class $n$ for every $n\in \mathbb{N}$. Then there exists an infinite nonnilpotent group with the above property and the conjecture 18.14 of $[5]$ is false.