\Bibitem{Tyu96} \by V.~N.~Tyutyanov \paper Products of $\pi$-nilpotent subgroups \jour Sb. Math. \yr 1996 \vol 187 \issue 9 \pages 1349--1354 \mathnet{http://mi.mathnet.ru/eng/sm159} \crossref{https://doi.org/10.1070/SM1996v187n09ABEH000159} \mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=1422384} \zmath{https://zbmath.org/?q=an:0867.20020} \isi{https://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=Publons&SrcAuth=Publons_CEL&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=A1996WE55900005} \scopus{https://www.scopus.com/record/display.url?origin=inward&eid=2-s2.0-0030300524}