Planarity and fixing number of inclusion graph of a nilpotent group

Abstract

The inclusion graph of a finite group [Formula: see text], written as [Formula: see text], is defined to be an undirected graph whose vertices are all nontrivial subgroups of [Formula: see text], and two distinct vertices [Formula: see text], [Formula: see text] are adjacent if and only if either [Formula: see text] or [Formula: see text]. For a graph [Formula: see text] with vertex set [Formula: see text], a set of vertices [Formula: see text] is called a fixing set of [Formula: see text] if the only automorphism of [Formula: see text] that fixes every element in [Formula: see text] is the identity. The fixing number of [Formula: see text] is the smallest size of a fixing set of [Formula: see text]. In this paper, we determine the finite nilpotent groups whose inclusion graphs are planar. Moreover, using the technique of characteristic matrices, we characterize the fixing sets and give the exact value on the fixing number of the inclusion graphs for finite cyclic groups.