On directable automata

@article{Cern1971OnDA,
  title={On directable automata},
  author={J{\'a}n Cern{\'y} and Alica Pirick{\'a} and Blanka Rosenauerov{\'a}},
  journal={Kybernetika},
  year={1971},
  volume={7},
  pages={289-298}
}