1. The measure algebra of a locally compact hypergroup;Dunkl, Charles F.;Trans. Amer. Math. Soc.,1973
2. Spaces with an abstract convolution of measures;Jewett, Robert I.;Advances in Math.,1975
3. K. A. Ross, Hypergroups and centers of measure algebras, A paraître dans Symposia Mathematica, Istituto Nazionale di alta Matematica.
4. Théorie axiomatique des hypergroupes;Spector, René;C. R. Acad. Sci. Paris S\'{e}r. A-B,1975
5. \bysame, Aperçu de la théorie des hypergroupes. Analyse Harmonique sur les Groupes de Lie, Séminaire Nancy-Strasbourg 1973-1975, Lecture Notes in Math. vol. 497, Springer-Verlag, Berlin and New York. 1975.