@article{KYB_1971_7_4_a1,
     author = {\v{C}ern\'y, J\'an and Pirick\'a, Alica and Rosenauerov\'a, Blanka},
     title = {On directable automata},
     journal = {Kybernetika},
     pages = {289--298},
     year = {1971},
     volume = {7},
     number = {4},
     mrnumber = {0302347},
     zbl = {0223.94029},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/KYB_1971_7_4_a1/}
}