@article{MASLO_1976_26_1_a3,
     author = {\v{S}marda, Bohumil},
     title = {Polars and {X-ideals} in semigroups},
     journal = {Mathematica slovaca},
     pages = {31--37},
     year = {1976},
     volume = {26},
     number = {1},
     mrnumber = {0427506},
     zbl = {0325.20063},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/MASLO_1976_26_1_a3/}
}