@article{ITA_1980__14_1_67_0,
     author = {Monien, Burkhard},
     title = {Two-way multihead automata over a one-letter alphabet},
     journal = {RAIRO. Informatique th\'eorique},
     pages = {67--82},
     publisher = {EDP-Sciences},
     volume = {14},
     number = {1},
     year = {1980},
     mrnumber = {570039},
     zbl = {0442.68039},
     language = {en},
     url = {http://www.numdam.org/item/ITA_1980__14_1_67_0/}
}