@article{AM2_1968__1_135975,
     author = {Kermit Sigman},
     title = {Medial {Topological} {Groupoids.}},
     journal = {Aequationes mathematicae},
     pages = {217--234},
     publisher = {mathdoc},
     volume = {1},
     year = {1968},
     zbl = {0164.33604},
     url = {http://geodesic.mathdoc.fr/item/AM2_1968__1_135975/}
}