Presentations

A Discussion of Some Open Problem in NF and Related Systems

See http://www.dpmms.cam.ac.uk/~tf/nf-in-the-bay-area.pdf
(current draught).

Symmetry, Comprehension and Indiscernibility of Urelements in NFU

Holmes will discuss symmetry as a
criterion for comprehension motivating NFU, with related questions
about term models of NFU and TST, and further discuss the demonstration
that the urelements in NFU are discernible in the "usual models of
NFU", in spite of the fact that symmetry arguments show that they are
indiscernible with respect to stratified formulas, because it turns out
that the membership relation of the nonstandard model of the usual set
theory underlying a "usual model" of NFU is definable in terms of the
membership relation of the model of NFU, so urelements can be
distinguished using properties of their original extensions.

An instance of Stratified Comprehension

∀As a bonus, our interpretation also satisfies some instances of Stratified Comprehension which are not strictly impredicative. For example, it verifies existence of Frege natural numbers.x_{1}…∀x_{n}∃y∀x(x∈y↔ φ(x,x_{1},…,x_{n}))