@article{10_4153_CJM_1991_013_2,
     author = {Bloom, Walter R. and Ressel, Paul},
     title = {Positive {Definite} and {Related} {Functions} on {Hypergroups}},
     journal = {Canadian journal of mathematics},
     pages = {242--254},
     year = {1991},
     volume = {43},
     number = {2},
     doi = {10.4153/CJM-1991-013-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1991-013-2/}
}