Denis Béchet Annie Foret Isabelle Tellier Learnability of Pregroup Grammars. 65-76 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3264&spage=65 2004 conf/icgi/2004 ICGI db/conf/icgi/icgi2004.html#BechetFT04