@article{ITA_1981__15_2_161_0,
     author = {Ehrenfeucht, A. and Rozenberg, G.},
     title = {FPOL systems generating counting languages},
     journal = {RAIRO. Informatique th\'eorique},
     pages = {161--173},
     publisher = {EDP-Sciences},
     volume = {15},
     number = {2},
     year = {1981},
     mrnumber = {618453},
     zbl = {0469.68077},
     language = {en},
     url = {http://archive.numdam.org/item/ITA_1981__15_2_161_0/}
}