Mitchell's Theorem Revisited

Abstract

Mitchell's theorem on the approachability ideal states that it is consistent relative to a greatly Mahlo cardinal that there is no stationary subset of $\omega_2 \cap \mathrm{cof}(\omega_1)$ in the approachability ideal $I[\omega_2]$. In this paper we give a new proof of Mitchell's theorem, deriving it from an abstract framework of side condition methods.