@article{MAT_1972_16_2_a2,
     author = {J. Tits},
     title = {Free subgroups in linear groups},
     journal = {Matematika},
     pages = {47--66},
     publisher = {mathdoc},
     volume = {16},
     number = {2},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1972_16_2_a2/}
}