@article{MASLO_1978_28_2_a3,
     author = {Porubsk\'y, \v{S}tefan},
     title = {On covering systems on rings},
     journal = {Mathematica slovaca},
     pages = {147--152},
     year = {1978},
     volume = {28},
     number = {2},
     mrnumber = {526852},
     zbl = {0375.13001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/MASLO_1978_28_2_a3/}
}