Jafarpour, Morteza; Chashiyani, Abdolah On special weak free (semi)hypergroups. (English) Zbl 1300.20062 J. Hyperstruct. 2, No. 1, 1-7 (2013). Summary: We study some properties of special weak free (semi)hypergroups and we generalize the Nielsen-Schreier theorem for the class of special weak free hypergroups. MSC: 20N20 Hypergroups 08B20 Free algebras Keywords:special weak free semihypergroups; special weak free hypergroups; join spaces; Nielsen-Schreier theorem PDFBibTeX XMLCite \textit{M. Jafarpour} and \textit{A. Chashiyani}, J. Hyperstruct. 2, No. 1, 1--7 (2013; Zbl 1300.20062)