@article{1102806637, author = {Brenner, J. L. and Charnow, A.}, title = {Free semigroups of $2\times 2$ matrices.}, journal = {Pacific J. Math.}, volume = {79}, number = {2}, year = {1978}, pages = { 57-69}, language = {en}, url = {http://dml.mathdoc.fr/item/1102806637} }
Brenner, J. L.; Charnow, A. Free semigroups of $2\times 2$ matrices.. Pacific J. Math., Tome 79 (1978) no. 2, pp. 57-69. http://gdmltest.u-ga.fr/item/1102806637/