“…Therefore it is natural to consider the opposite situation, that is the groups whose ascendant subgroups are permutable. A group G is said to be an AP -group if every ascendant subgroup of G is permutable in G. These groups are very close to the groups in which the relation to be a permutable subgroup is transitive (studied in [3] for a class of periodic radical groups). A group G is said to be a P T -group if permutability is a transitive relation in G, that is, if K is a permutable subgroup of H and H is a permutable subgroup of G, then K is a permutable subgroup of G. We note that, if G is an AP -group, then clearly G is a P T -group, because the relation to be an ascendant subgroup is transitive.…”