The permutation method was first applied to NF by Scott; other workers have published results ([2], [3]; or see [4] for a survey). Some of the results proved here have a more metalogical character than most previously yielded by this method. Hinnion and Petry (unpublished, but see [4]) proved that the existence of objects x such that x = {y: x∈y} is consistent with NF. (The significance of this is that the operation that sends x to {y: x∈y} respects ∈ and is thus an embedding.) It is demonstrated below that the existence of such objects is independent of the axioms of NF.

The existence of nontrivial automorphisms of the universe is not an interesting possibility in ZF, since it contradicts wellfoundedness. Similar auguments are not available in NF, however, and it is shown below that if NF + AC for pairs is consistent, then we can consistently add an axiom stating that there is a ∈-automorphism of the universe that is a set of the model. (In the proof given below, the automorphism is in fact of order 2, but natural enrichments of the construction enable one to find automorphisms of other orders with suitable versions of choice as additional hypotheses.)