@article{PMFA_1957_2_5_a1,
     author = {Perkal, Julian},
     title = {O souborech materi\'aln{\'\i}ch bod\r{u} a abstraktn{\'\i}ch bod\r{u} v p\v{r}{\'\i}rodov\v{e}deck\'ych zkoum\'an{\'\i}ch},
     journal = {Pokroky matematiky, fyziky a astronomie},
     pages = {513--522},
     year = {1957},
     volume = {2},
     number = {5},
     language = {cs},
     url = {http://geodesic.mathdoc.fr/item/PMFA_1957_2_5_a1/}
}