1. A. N. Skiba, “On critical formations,” Dokl. Akad. Nauk. Belorus. SSR, 27, No. 9, 780–782 (1983).
2. L. A. Shemetkov, “Screens of graded formations,” in: Proceedings of the All-Union Symposium on Group Theory [in Russian], Naukova Dumka, Kiev (1980), pp. 37–50.
3. A. N. Skiba, “On critical formations,” in: Infinite Groups and Related Algebraic Structures [in Russian], Kiev (1993), pp. 258–268.
4. V. M. Sel’kin and A. N. Skiba, “On hereditary critical formations,” Sib. Mat. Zh., 37, No. 5, 1145–1153 (1996).
5. L. A. Shemetkov and A. N. Skiba, Formations of Algebraic Systems [in Russian], Nauka, Moscow (1989).