@article{GDZPPN002022451, title = {Medial Topological Groupoids.}, journal = {Aequationes mathematicae}, volume = {1}, year = {1968}, pages = {217-234}, zbl = {0164.33604}, url = {http://dml.mathdoc.fr/item/GDZPPN002022451} }
Sigman, Kermit. Medial Topological Groupoids.. Aequationes mathematicae, Tome 1 (1968) pp. 217-234. http://gdmltest.u-ga.fr/item/GDZPPN002022451/