@article{ITA_1979__13_2_189_0, author = {Greibach, S. A.}, title = {One counter languages and the chevron operation}, journal = {RAIRO. Informatique th\'eorique}, pages = {189--194}, publisher = {EDP-Sciences}, volume = {13}, number = {2}, year = {1979}, zbl = {0441.68081}, mrnumber = {543940}, language = {en}, url = {http://www.numdam.org/item/ITA_1979__13_2_189_0/} }