@article{PMFA_1990_35_5_a6,
     author = {Oku\v{n}, L. B.},
     title = {O pojmu hmotnost {(Hmotnost,} energie, relativita)},
     journal = {Pokroky matematiky, fyziky a astronomie},
     pages = {285--301},
     year = {1990},
     volume = {35},
     number = {5},
     language = {cs},
     url = {http://geodesic.mathdoc.fr/item/PMFA_1990_35_5_a6/}
}