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@article{MZ_1969__112_171241, author = {Trevor Evans}, title = {Schreier {Varieties} of {Semigroups.}}, journal = {Mathematische Zeitschrift}, pages = {296--299}, publisher = {mathdoc}, volume = {112}, year = {1969}, zbl = {0175.29301}, url = {http://geodesic.mathdoc.fr/item/MZ_1969__112_171241/} }
Trevor Evans. Schreier Varieties of Semigroups.. Mathematische Zeitschrift, Tome 112 (1969), pp. 296-299. http://geodesic.mathdoc.fr/item/MZ_1969__112_171241/