@article{GDZPPN001254308, title = {A generalization of the bicyclic semigroup.}, journal = {Semigroup forum}, volume = {20}, year = {1980}, pages = {13-26}, zbl = {0449.20062}, url = {http://dml.mathdoc.fr/item/GDZPPN001254308} }
Adair, C.L. A generalization of the bicyclic semigroup.. Semigroup forum, Tome 20 (1980) pp. 13-26. http://gdmltest.u-ga.fr/item/GDZPPN001254308/