Maciej Kandulski Derived Tree Languages of Nonassociative Lambek Categorial Grammars with Product. 349-362 2003 55 Fundam. Inform. 3-4 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=55&issue=3&spage=349 db/journals/fuin/fuin55.html#Kandulski03