@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/}
}