English

On a Theorem by Bezboruah & Shepherdson

Logic 2026-05-06 v2

Abstract

We discuss an incompleteness result proven by Bezboruah and Shepherdson. This result tells us that the weak theory PA{\sf PA}^- does not prove the consistency of any theory (under certain assumptions explained in the paper). Kreisel argued that such a result is not meaningful. We discuss Kreisel's objection and conclude that his argument does not hold water. We compare Pudl\'ak's extension of the Second Incompleteness Theorem with the Bezboruah-Sheperdson Theorem. Finally, we reprove the Bezboruah-Sheperdson Theorem for a sequence coding based on an insight of Nielsen and Markov.

Cite

@article{arxiv.2603.06068,
  title  = {On a Theorem by Bezboruah & Shepherdson},
  author = {Albert Visser},
  journal= {arXiv preprint arXiv:2603.06068},
  year   = {2026}
}

Comments

A mistake towards the end of the paper was repaired. The correct result is now given in Theorem 4.6

R2 v1 2026-07-01T11:06:27.841Z