@article{GDZPPN002538709, title = {On free commutative groupoids.}, journal = {Publications de l'Institut Math\'ematique [Elektronische Ressource]}, volume = {41}, year = {1980}, pages = {209-224}, zbl = {0472.20026}, url = {http://dml.mathdoc.fr/item/GDZPPN002538709} }
Presic, M.D. On free commutative groupoids.. Publications de l'Institut Mathématique [Elektronische Ressource], Tome 41 (1980) pp. 209-224. http://gdmltest.u-ga.fr/item/GDZPPN002538709/