@Article{TALN-2012-BDF-TCS,
 author       = {Denis B\'echet and Alexandre Dikovsky and Annie Foret},
 title        = {Categorial grammars with iterated types form a strict hierarchy of k-valued languages},
 journal      = {Theoretical Computer Science},
 volume       = {450},
 number       = {0},
 pages        = {22--30},
 year         = {2012},
 note         = {Selection of articles from Implementation and Application of Automata (CIAA 2011)},
 ISSN         = {0304-3975},
 DOI          = {10.1016/j.tcs.2012.04.024},
 URL          = {http://www.sciencedirect.com/science/article/pii/S0304397512003799}
}