k-valued non-associative lambek grammars (without product) form a strict hierarchy of languages

  • Authors:
  • Denis Béchet;Annie Foret

  • Affiliations:
  • LINA – FRE 2729, Université de Nantes & CNRS, Nantes Cedex 03, France;IRISA, Université de Rennes 1, Rennes Cedex, France

  • Venue:
  • LACL'05 Proceedings of the 5th international conference on Logical Aspects of Computational Linguistics
  • Year:
  • 2005

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Abstract

The notion of k-valued categorial grammars where a word is associated to at most k types is often used in the field of lexicalized grammars as a fruitful constraint for obtaining several properties like the existence of learning algorithms. This principle is relevant only when the classes of k-valued grammars correspond to a real hierarchy of languages. This paper establishes the relevance of this notion for two related grammatical systems. In the first part, the classes of k-valued non-associative Lambek (NL) grammars without product is proved to define a strict hierarchy of languages. The second part introduces the notion of generalized functor argument for non-associative Lambek (NL∅) calculus without product but allowing empty antecedent and establishes also that the classes of k-valued (NL∅) grammars without product form a strict hierarchy of languages.