@article{ITA_1990__24_5_459_0,
     author = {Neraud, Jean},
     title = {Elementariness of a finite set of words is {co-NP-complete}},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {459--470},
     publisher = {EDP-Sciences},
     volume = {24},
     number = {5},
     year = {1990},
     mrnumber = {1080501},
     zbl = {0704.68065},
     language = {en},
     url = {http://www.numdam.org/item/ITA_1990__24_5_459_0/}
}