Intercalation theorems for tree transducer languages

  • Authors:
  • C. Raymond Perrault

  • Affiliations:
  • -

  • Venue:
  • STOC '75 Proceedings of seventh annual ACM symposium on Theory of computing
  • Year:
  • 1975

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Abstract

We develop intercalation lemmas for the computations of the top-down tree transducers defined by Rounds [15] and Thatcher [17]. These lemmas are used to prove necessary conditions for languages all of whose strings are of exponential length to be tree transducer languages. The language {ww:w&egr;{a,b}*, ¦w¦&equil;2n,n≥0}, which is generable by the composition of two transducers, is shown not to be generable by one. The proof technique applies to bottom-up transducers as well. The results are related to some subclasses of Woods' Augmented Transition Networks [18] characterized elsewhere in terms of tree transducer languages [14].