@article{RMF_2009_84_4_a1,
     author = {Katrno\v{s}ka, Franti\v{s}ek and K\v{r}{\'\i}\v{z}ek, Michal},
     title = {Kleinova \v{c}ty\v{r}grupa},
     journal = {Rozhledy matematicko-fyzik\'aln{\'\i}},
     pages = {4--9},
     year = {2009},
     volume = {84},
     number = {4},
     language = {cs},
     url = {http://geodesic.mathdoc.fr/item/RMF_2009_84_4_a1/}
}