@article{GDZPPN002487926, title = {On a General Associativity Law in Groupoids.}, journal = {Monatshefte f\"ur Mathematik}, volume = {114}, year = {1992}, pages = {51-58}, zbl = {0768.20032}, url = {http://dml.mathdoc.fr/item/GDZPPN002487926} }
Niemenmaa, Markku; Kepka, Tomas. On a General Associativity Law in Groupoids.. Monatshefte für Mathematik, Tome 114 (1992) pp. 51-58. http://gdmltest.u-ga.fr/item/GDZPPN002487926/