Анотація:
A subgroup H of the group G is said to be permutable (or quasinormal) in G, in symbols H per G, if HK = KH for all subgroups K of G. We consider periodic locally soluble FC-groups, in which the permutability is a transitive relation. S-permutability is a rather wide generalization of the usual permutability. We show some properties of S-permutability for infinite periodic FC-groups.