@article{GDZPPN00126107X, title = {Semigroups in the universal covering of SL(2).}, journal = {Semigroup forum}, volume = {43}, year = {1991}, pages = {33-44}, zbl = {0736.22005}, url = {http://dml.mathdoc.fr/item/GDZPPN00126107X} }
Neeb, K.H. Semigroups in the universal covering of SL(2).. Semigroup forum, Tome 43 (1991) pp. 33-44. http://gdmltest.u-ga.fr/item/GDZPPN00126107X/