@article{KYB_1978_14_6_a1,
     author = {P\u{a}un, Gheorghe},
     title = {Two infinite hierarchies of languages defined by branching grammars},
     journal = {Kybernetika},
     pages = {397--407},
     year = {1978},
     volume = {14},
     number = {6},
     mrnumber = {529192},
     zbl = {0394.68052},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/KYB_1978_14_6_a1/}
}