@article{GDZPPN002405474, title = {Schreier Varieties of Semigroups.}, journal = {Mathematische Zeitschrift}, volume = {111}, year = {1969}, pages = {296-299}, zbl = {0175.29301}, url = {http://dml.mathdoc.fr/item/GDZPPN002405474} }
Evans, Trevor. Schreier Varieties of Semigroups.. Mathematische Zeitschrift, Tome 111 (1969) pp. 296-299. http://gdmltest.u-ga.fr/item/GDZPPN002405474/