Abstract

Partial models of the theory New Foundations (NF) introduced by Quine have already appeared in the literature, but in every model the membership set of NF is missing. On the other hand, Jensen showed that "NF + Urelements" is consistent with respect to ZF and, in the model built there, the membership set of the theory exists. Here we build a partial model of NF from the one of Jensen in which the membership set exists.