The Structure of EAP-Groups and Self-Autopermutable Subgroups

A subgroup H of a given group G is said to be autopermutable, if HH (α) = H (α) H for all α ∈ Aut(G). We also call H a self-autopermutable subgroup of G, when HH (α) = H (α) H implies that H (α) = H. Moreover, G is said to be EAP-group, if every subgroup of G is autopermutable. One notes that if α runs over the inner automorphisms of the group, one obtains the notions of conjugate-permutability, self-conjugate-permutability, and ECP-groups, which were studied by Foguel in 1997, Li and Meng in 2007, and Xu and Zhang in 2005, respectively. In the present paper, we determine the structure of a finite EAP-group when its centre is of index 4 in G. We also show that self-autopermutability and characteristic properties are equivalent for nilpotent groups.