@article{CMUC_1985_26_2_a2,
     author = {T\r{u}ma, Ji\v{r}{\'\i}},
     title = {A simple geometric proof of a theorem on $M_n$},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {233--239},
     year = {1985},
     volume = {26},
     number = {2},
     mrnumber = {803919},
     zbl = {0567.08001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1985_26_2_a2/}
}