Groups in which the commutant is generated by invariant cyclic subgroups

We study groups in which the commutant is generated by invariant cyclic subgroups. Existence of a hypercentral coradical in a periodic group is proved and a completability criterion is derived for some subgroups of the coradical.Kiev Polytechnical Institute. Translated from Vychislitel'naya i Prikladnaya Matematika, No. 74, pp. 85–88, 1992;