“…For chronological development of this approach and for background information on varieties of groups or on wreath products we refer to [20,21,8,2,3,25,6] and to literature cited therein. Generalizing some results in the cited literature, we in [13]- [18] were able to suggest criteria classifying all the cases when ( * ) holds for groups from certain classes of groups: abelian groups, p-groups, nilpotent groups of finite exponent, etc. (see, in particular, very brief outline of results in Section 5 of [18]).…”