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@article{SF_1991__42_3_135073, author = {N. Hindman and J. Pym}, title = {Closure of singly generated subsemigroups of {S.}}, journal = {Semigroup forum}, pages = {147--154}, publisher = {mathdoc}, volume = {42}, number = {3}, year = {1991}, zbl = {0721.22001}, url = {http://geodesic.mathdoc.fr/item/SF_1991__42_3_135073/} }
N. Hindman; J. Pym. Closure of singly generated subsemigroups of S.. Semigroup forum, Tome 42 (1991) no. 3, pp. 147-154. http://geodesic.mathdoc.fr/item/SF_1991__42_3_135073/