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On the Effect of the IO-Substitution on the Parikh Image of Semilinear Full AFLs

  • Pierre BourreauEmail author
Article
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Abstract

Back in the 1980’s, the class of mildly context-sensitive formalisms was introduced so as to capture the syntax of natural languages. While the languages generated by such formalisms are constrained by the constant-growth property, the most well-known and used ones—like tree-adjoining grammars or multiple context-free grammars—generate languages which verify the stronger property of being semilinear. In (Bourreau et al. 2012), the operation of IO-substitution was created so as to exhibit mildly-context sensitive classes of languages which are not semilinear. In the present article, we extend the notion of semilinearity, and characterize the Parikh image of the languages in IO(L), the closure of a class L of semilinear languages under IO-substitution, as universally-semilinear. Based on this result and on the work of Fischer on macro-grammars, we then show that IO(L) is not closed under inverse homomorphism when L is closed under inverse homomorphism, and encompasses the class of regular languages. This result proves that IO(MCFL) is not a full AFL, where \(\mathbf {MCFL}\) denotes the class of multiple context-free languages, closing an open question in Bourreau et al. (2012). More importantly, our proof gives an insight into the relation between the non-closure under inverse homomorphism of \(\mathbf {IO(MCFL)}\) and how IO-substitution breaks semilinearity.

Keywords

Formal languages Mildly context-sensitive formalisms  Semilinearity Constant-growth IO macro-grammars Multiple context-free grammars  Abstract family of languages 

Notes

Acknowledgments

This work was funded by the Deutsche Forchungsgemeinschaft, under the project SFB 991 “Die Struktur von Repräsentationen in Sprache, Kognition und Wissenschaft”. I am thankful to Sylvain Salvati for the motivating discussions on this topic; to Laura Kallmeyer for her insights on the notions of universally-linear sets; and to Christian Wurm who helped me to improve the formal definitions with his feedbacks. The responsibility for any mistakes contained herein rests solely on me.

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Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.Institut für Sprache und InformationHeine-Heinrich Universität DüsseldorfDüsseldorfGermany

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