On the Uniform Learnability of Approximations to Non-Recursive Functions

  • Authors:
  • Frank Stephan;Thomas Zeugmann

  • Affiliations:
  • -;-

  • Venue:
  • ALT '99 Proceedings of the 10th International Conference on Algorithmic Learning Theory
  • Year:
  • 1999

Quantified Score

Hi-index 0.00

Visualization

Abstract

Blum and Blum (1975) showed that a class B of suitable recursive approximations to the halting problem is reliably EX-learnable. These investigations are carried on by showing that B is neither in NUM nor robustly EX-learnable. Since the definition of the class B is quite natural and does not contain any self-referential coding, B serves as an example that the notion of robustness for learning is quite more restrictive than intended. Moreover, variants of this problem obtained by approximating any given recursively enumerable set A instead of the halting problem K are studied. All corresponding function classes U(A) are still EX-inferable but may fail to be reliably EX-learnable, for example if A is non-high and hypersimple. Additionally, it is proved that U(A) is neither in NUM nor robustly EX-learnable provided A is part of a recursively inseparable pair, A is simple but not hypersimple or A is neither recursive nor high. These results provide more evidence that there is still some need to find an adequate notion for "naturally learnable function classes."