1. S. H. Dalalyan, “On hypergroups, prenormal subgroups and simplest groups,” in Proceedings of the Conference Dedicated to 90-Aniversary of M. M. Djrbashyan, Yerevan, 2008, pp. 27–28.
2. S. H. Dalalyan, “Hypergroups over the group and generalizations of Schreier’s theorem on group extensions,” arXiv:09409000 [math.Gr] (2014).
3. S. H. Dalalyan, “Structures induced on transversals to a subgroup of a group and hypergroups over the group,” arXiv:1508.00517v2 [math.GR] (2015).
4. G. L. Litvinov, Hypergroups and Hypergroup Algebras (VINITI, Moscow, 1985), Vol. 26, pp. 57–106 [in Russian].
5. F. Marty, “Sur une generalisation de la notion de group,” in Proceedings of the 8th Congress des Mathematiciens Scandinaves, Stockholm, 1934, pp. 45–49.