- 633 名前：]
Adding urelements to the system New Foundations (NF) to produce NFU has surprising consequences.
Quine atoms
An alternative approach to urelements is to consider them, instead of as a type of object other than sets, as a particular type of set. Quine atoms (named after Willard Van Orman Quine) are sets that only contain themselves, that is, sets that satisfy the formula x = {x}.[7] [] - [ここ壊れてます]
