1. Baer, R.: Situation der Untergruppen und Struktur der Gruppe. S.B. Heidelberg Akad. Mat. Nat. Klasse2, 12?17 (1933)
2. ?ernikov, S.N.: On investigations of groups with properties prescribed on their subgroups. Ukrain. Mat. Z.21, 193?209 (1969)
3. ?ernikov, S.N.: Infinite non-Abelian groups with an invariance condition for infinite non-Abelian subgroups. Dokl. Akad. Nauk SSSR134, 1280?1283 (1970)
4. ?ernikov, S.N.: Infinite nonabelian groups in which all infinite non-abelian subgroups are invariant. Ukrain. Mat. Z.,23, 498?518 (1971)
5. Dedekind, R.: Über Gruppen, deren sämtliche Teiler Normalteiler sind. Math. Ann.48, 548?561 (1897).