Hierarchy of Monotonically Computable Real Numbers

  • Authors:
  • Robert Rettinger;Xizhong Zheng

  • Affiliations:
  • -;-

  • Venue:
  • MFCS '01 Proceedings of the 26th International Symposium on Mathematical Foundations of Computer Science
  • Year:
  • 2001

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Abstract

A real number x is called h-monotonically computable (h- mc), for some function h, if there is a computable sequence (xs)s∈N of rational numbers such that h(n)|x - xn| ≥ |x - xm| for any m ≥ n. x is called ω-monotonically computable (ω-mc) if it is h-mc for some recursive function h and, for any c ∈ R, x is c-mcif it is h-mcfor the constant function h ≡ c. In this paper we discuss the properties of c-mc and ω-mc real numbers. Among others we will show a hierarchy theorem of c-mc real numbers that, for any constants c2 c1 ≥ 1, there is a c2-mcr eal number which is not c1-mca nd that there is an ω-mc real number which is not c-mc for any c ∈ R. Furthermore, the class of all ω-mcr eal numbers is incomparable with the class of weakly computable real numbers which is the arithmetical closure of semi-computable real numbers.