@article{ITA_1991__25_4_305_0,
     author = {Madonia, M. and Salemi, S. and Sportelli, T.},
     title = {On $z$-submonoids and $z$-codes},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {305--322},
     publisher = {EDP-Sciences},
     volume = {25},
     number = {4},
     year = {1991},
     mrnumber = {1134385},
     zbl = {0764.68089},
     language = {en},
     url = {http://www.numdam.org/item/ITA_1991__25_4_305_0/}
}