Comparing C.E. Sets Based on Their Settling Times

  • Authors:
  • Barbara F. Csima

  • Affiliations:
  • Department of Pure Mathematics, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

  • Venue:
  • CiE '07 Proceedings of the 3rd conference on Computability in Europe: Computation and Logic in the Real World
  • Year:
  • 2007

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Abstract

To each computable enumerable (c.e.) set Awith aparticular enumeration {As}sεω,there is associated a settling function mA(x), where mA(x) is the last stage when a numberless than or equal to xwas enumerated into A. In[7], R.W. Robinson classified the complexity of c.e. sets into twogroups of complexity based on whether or not the settling functionwas dominant. An extension of this idea to a more refined orderingof c.e. sets was first introduced by Nabutovsky and Weinberger in[6] and Soare [9], for application to differential geometry. Therethey defined one c.e. set Ato settling time dominateanother c.e. set B(B stA) if for every computable function f, for allbut finitely many x, mB(x) f(mA(x)). In [4] Csima and Soareintroduced a stronger ordering, where BsstAif for all computable fandg, for almost all x, mB(x) f(mA(g(x))). We give a survey ofthe known results about these orderings, make some observations,and outline the open questions.