@article{PORMA_2004__61_3_52996,
     author = {do Rocio, Osvaldo Germano and Santana, Alexandre J.},
     title = {Free groups of semigroups in semi-simple {Lie} groups.},
     journal = {Portugaliae mathematica},
     pages = {339--354},
     publisher = {mathdoc},
     volume = {61},
     number = {3},
     year = {2004},
     zbl = {1106.22004},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_2004__61_3_52996/}
}