1. Ore O., “Contributions in the theory of groups of finite order,” Duke Math. J., vol. 5, no. 2, 431–460 (1939).
2. Doerk K. and Hawkes T., Finite Soluble Groups, De Gruyter, Berlin and New York (1992).
3. Stonehewer S.E., “Permutable subgroups of infinite groups,” Math. Z., vol. 125, no. 1, 1–16 (1972).
4. Ito N. and Szep J., “Uber die Quasinormalteiler von endlichen Gruppen,” Acta Sci. Math., vol. 23, no. 1, 168–170 (1962).
5. Isaacs I.M., Finite Group Theory, Amer. Math. Soc., Providence (2008) (Graduate Texts Math.; vol. 92).