@article{ARM_1980_16_4_a8,
     author = {Vor\'a\v{c}, Franti\v{s}ek},
     title = {Subgroups and normal subgroups as systems of ideals},
     journal = {Archivum mathematicum},
     pages = {239--244},
     year = {1980},
     volume = {16},
     number = {4},
     mrnumber = {0594472},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_1980_16_4_a8/}
}