Considerations on the subgroup commutativity degree and related notions

The concept of subgroup commutativity degree of a finite group $G$ is arising interest in several areas of group theory in the last years, since it gives a measure of the probability that a randomly picked pair $(H,K)$ of subgroups of $G$ satisfies the condition $HK=KH$. In this paper, a stronger notion is studied and relations with the commutativity degree are found.