How Incomputable is the Separable Hahn-Banach Theorem?

  • Authors:
  • Guido Gherardi;Alberto Marcone

  • Affiliations:
  • Dipartimento di Filosofia, Università di Bologna, Italy;Dipartimento di Matematica e Informatica, Università di Udine, Italy

  • Venue:
  • Electronic Notes in Theoretical Computer Science (ENTCS)
  • Year:
  • 2008

Quantified Score

Hi-index 0.00

Visualization

Abstract

We investigate some basic connections between reverse mathematics and computable analysis. In particular, we show how to use Weak Konig's Lemma within the framework of computable analysis to classify incomputable functions of low complexity. By defining the multi-valued function Sep and through the definition of a natural notion of reducibility for multi-valued functions, we obtain a computational counterpart of the subsystem of second order arithmetic WKL"0. We study analogies and differences between WKL"0 and the class of Sep-computable multi-valued functions. We use these notions to provide a method to determine the computational complexity of the Hahn-Banach Extension Theorem.