@article{GDZPPN001260871, title = {Closure of singly generated subsemigroups of S.}, journal = {Semigroup forum}, volume = {43}, year = {1991}, pages = {147-154}, zbl = {0721.22001}, url = {http://dml.mathdoc.fr/item/GDZPPN001260871} }
Hindman, N.; Pym, J. Closure of singly generated subsemigroups of S.. Semigroup forum, Tome 43 (1991) pp. 147-154. http://gdmltest.u-ga.fr/item/GDZPPN001260871/