@article{ARM_2004_40_4_a7,
     author = {Pol\'ak, Libor},
     title = {A classification of rational languages by semilattice-ordered monoids},
     journal = {Archivum mathematicum},
     pages = {395--406},
     year = {2004},
     volume = {40},
     number = {4},
     mrnumber = {2129961},
     zbl = {1112.68098},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_2004_40_4_a7/}
}