Randomness and universal machines

  • Authors:
  • Santiago Figueira;Frank Stephan;Guohua Wu

  • Affiliations:
  • Department of Computer Science, FCEyN, University of Buenos Aires, Argentina;Department of Mathematics, National University of Singapore, 2 Science Drive 2, Singapore 117543, Singapore;School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637616, Singapore

  • Venue:
  • Journal of Complexity
  • Year:
  • 2006

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Abstract

The present work investigates several questions from a recent survey of Miller and Nies related to Chaitin's @W numbers and their dependence on the underlying universal machine. Furthermore, the notion @W"U[X]=@?"p":"U"("p")"@7"@?"X2^-^|^p^| is studied for various sets X and universal machines U. A universal machine U is constructed such that for all x, @W"U[{x}]=2^1^-^H^(^x^). For such a universal machine there exists a co-r.e. set X such that @W"U[X] is neither left-r.e. nor Martin-Lof random. Furthermore, one of the open problems of Miller and Nies is answered completely by showing that there is a sequence U"n of universal machines such that the truth-table degrees of the @W"U"""n form an antichain. Finally, it is shown that the members of hyperimmune-free Turing degree of a given @P"1^0-class are not low for @W unless this class contains a recursive set.