@article{DAN_1968_182_5_a5,
     author = {A. A. Letichevskii},
     title = {Equivalence of ultimate state automata relative to a free semigroup with right zero},
     journal = {Doklady Akademii Nauk},
     pages = {1007--1009},
     publisher = {mathdoc},
     volume = {182},
     number = {5},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_182_5_a5/}
}