New Foundations
AXIOMATIC SET THEORY PERMITTING SET COMPREHENSION BY STRATIFIED FORMULAE, HENCE WITH A UNIVERSAL SET, BUT IN WHICH THE SINGLETON MAP 𝑥↦{𝑥} FAILS TO EXIST
New foundations; Typed set theory; New Foundations for Mathematical Logic
In mathematical logic, New Foundations (NF) is an axiomatic set theory, conceived by Willard Van Orman Quine as a simplification of the theory of types of Principia Mathematica. Quine first proposed NF in a 1937 article titled "New Foundations for Mathematical Logic"; hence the name.