@article{ARM_1970_6_3_a2,
     author = {Novotn\'y, Miroslav},
     title = {On a class of languages},
     journal = {Archivum mathematicum},
     pages = {155--170},
     year = {1970},
     volume = {6},
     number = {3},
     mrnumber = {0319421},
     zbl = {0236.68030},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_1970_6_3_a2/}
}