Finite groups with the same join graph as a finite nilpotent group

Abstract

Given a finite group $G,$ we denote by $\Delta(G)$ the graph whose vertices are the proper subgroups of $G$ and in which two vertices $H$ and $K$ are joined by an edge if and only if $G=\langle H,K\rangle.$ We prove that if there exists a finite nilpotent group $X$ with $\Delta(G)\cong \Delta(X),$ then $G$ is supersoluble.