NF is Consistent

Abstract

In this paper we will present a proof of the consistency of Quine's set theory "New Foundations" (hereinafter NF), so-called after the title of the 1937 paper in which it was introduced. This version takes the approach of building a model of tangled type theory rather than a model of the usual set theory without choice with a tangled web of cardinals; further, details of the construction are refined due to interaction with the now complete verification in Lean by the second author.