@article{1183526325, author = {Gottlieb, D. H. and Rothman, N. J.}, title = {Contractibility of certain semigroups}, journal = {Bull. Amer. Math. Soc.}, volume = {70}, number = {6}, year = {1964}, pages = { 756-757}, language = {en}, url = {http://dml.mathdoc.fr/item/1183526325} }
Gottlieb, D. H.; Rothman, N. J. Contractibility of certain semigroups. Bull. Amer. Math. Soc., Tome 70 (1964) no. 6, pp. 756-757. http://gdmltest.u-ga.fr/item/1183526325/