@article{ITA_2006__40_1_15_0,
     author = {Borel, Jean-Pierre and Reutenauer, Christophe},
     title = {On {Christoffel} classes},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {15--27},
     publisher = {EDP-Sciences},
     volume = {40},
     number = {1},
     year = {2006},
     doi = {10.1051/ita:2005038},
     mrnumber = {2197281},
     zbl = {1085.68116},
     language = {en},
     url = {http://archive.numdam.org/articles/10.1051/ita:2005038/}
}