1. N. Ito, “Ueber das Produkt von zwei abelschen Gruppen,”Math. Z.,62, No. 4, 400–401 (1955).
2. B. Kolman, “Semi-modular Lie algebras”,J. Sci. Hiroshima Univ., Ser. A1,29, 149–163 (1965).
3. Kourovka Notebook (Unsolved Problems in Group Theory) [in Russian], 11th ed., Institute of Mathematics, Academy of Sciences of the USSR, Siberian Division, Novosibirsk (1990).
4. O. H. Kegel, “On the solvability of some factorized linear groups,”Ill. J. Math.,9, No. 3, 535–547 (1965).
5. Yu. Bahturin, and O. H. Kegel, “Universal sums of Abelian subalgebras,”Commun. Algebra,23, 2975–2990 (1995).