@article{KYB_1969_5_1_a4,
     author = {Kr\'al, Jaroslav},
     title = {On multiple grammars},
     journal = {Kybernetika},
     pages = {60--85},
     year = {1969},
     volume = {5},
     number = {1},
     mrnumber = {0250802},
     zbl = {0175.27703},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/KYB_1969_5_1_a4/}
}