On small hard leaf languages

  • Authors:
  • Falk Unger

  • Affiliations:
  • Centrum voor Wiskunde en Informatica (CWI), Amsterdam, The Netherlands

  • Venue:
  • MFCS'05 Proceedings of the 30th international conference on Mathematical Foundations of Computer Science
  • Year:
  • 2005
  • Very sparse leaf languages

    MFCS'06 Proceedings of the 31st international conference on Mathematical Foundations of Computer Science

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Abstract

This paper deals with balanced leaf language complexity classes, introduced independently in [1] and [14]. We propose the seed concept for leaf languages, which allows us to give “short” representations for leaf words. We then use seeds to show that leaf languages A with NP⊆BLeafP(A) cannot be polylog-sparse (i.e. censusA ∈ O(logO(1))), unless PH collapses. We also generalize balanced ≤$^{P,{bit}}_{m}$-reductions, which were introduced in [6], to other bit-reductions, for example (balanced) truth-table- and Turing-bit-reductions. Then, similarly to above, we prove that NP and Σ$^{P}_{\rm 2}$ cannot have polylog-sparse hard sets under those balanced truth-table- and Turing-bit-reductions, if the polynomial-time hierarchy is infinite.