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@article{SF_1971__2_133813, author = {H.E. Scheiblich}, title = {A characterization of a free elementary semigroup.}, journal = {Semigroup forum}, pages = {76--79}, publisher = {mathdoc}, volume = {2}, year = {1971}, zbl = {0226.20064}, url = {https://geodesic-test.mathdoc.fr/item/SF_1971__2_133813/} }
H.E. Scheiblich. A characterization of a free elementary semigroup.. Semigroup forum, Tome 2 (1971), pp. 76-79. https://geodesic-test.mathdoc.fr/item/SF_1971__2_133813/