Rigid grammars in the Associative-Commutative Lambek Calculus are not learnable Christophe Costa Florencio author 2003-04 text 10th Conference of the European Chapter of the Association for Computational Linguistics Ann Copestake editor Jan Hajič editor Association for Computational Linguistics Budapest, Hungary conference publication florencio-2003-rigid https://aclanthology.org/E03-1033/ 2003-04