Abstract:
Let $\pi$ be a set of prime numbers. We say that a finite group $G$ is a $\mathcal D_\pi$-group if all of its maximal $\pi$-subgroups are conjugate. Question 17.44(b) in Unsolved Problems in Group Theory, The Kourovka Notebook, asks whether an overgroup of a $\pi$-Hall subgroup of a $\mathcal D_\pi$-group is always a $\mathcal D_\pi$-group. We give an affirmative answer to this question in the case where $2\in\pi$.
Keywords:finite group, $\pi$-Hall subgroup, $\mathcal D_\pi$-group, group of Lie type, finite simple group, maximal subgroup of odd index.