@article{10_21136_CMJ_1979_101588,
     author = {Porubsk\'y, \v{S}tefan},
     title = {On the density of certain sets in arithmetical semigroups},
     journal = {Czechoslovak Mathematical Journal},
     pages = {148--152},
     publisher = {mathdoc},
     volume = {29},
     number = {1},
     year = {1979},
     doi = {10.21136/CMJ.1979.101588},
     mrnumber = {518150},
     zbl = {0439.10033},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1979.101588/}
}