1. Corsini, P.: Prolegomena of Hypergroup Theory. Aviani Editore, Tricesimo (1993)
2. Corsini, P., Leoreanu, V.: Applications of Hyperstructure Theory. Kluwer Academical Publications, Dordrecht (2003)
3. Davvaz, B.: Semihypergroup Theory, p. viii+156. Elsevier/Academic Press, London (2016)
4. Davvaz, B., Bardestani, F.: Hypergroups of type $$U$$ on the right of size six. Arab. J. Sci. Eng. 36, 487–499 (2011)
5. Davvaz, B.: Polygroup Theory and Related Systems. World Scientific Publishing Co. Pte. Ltd., Hackensack, NJ (2013)