[過去ﾛｸﾞ] 現代数学の系譜 工学物理雑談 古典ガロア理論も読む77 (1002ﾚｽ)
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119(1): 現代数学の系譜 雑談 古典ガロア理論も読む ◆e.a0E5TtKE 2019/09/13(金)23:21 ID:Ct8Lh9wH(13/15) AAS
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外部ﾘﾝｸ:en.wikipedia.org
Urelement
(抜粋)
In set theory, a branch of mathematics, an urelement or ur-element (from the German prefix ur-, 'primordial') is an object that is not a set, but that may be an element of a set. Urelements are sometimes called "atoms" or "individuals."

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120: 現代数学の系譜 雑談 古典ガロア理論も読む ◆e.a0E5TtKE 2019/09/13(金)23:23 ID:Ct8Lh9wH(14/15) AAS
>>119

つづき

Adding urelements to the system New Foundations (NF) to produce NFU has surprising consequences.
In particular, Jensen proved[5] the consistency of NFU relative to Peano arithmetic; meanwhile, the consistency of NF relative to anything remains an open problem, pending verification of Holmes's proof of its consistency relative to ZF.
Moreover, NFU remains relatively consistent when augmented with an axiom of infinity and the axiom of choice.
Meanwhile, the negation of the axiom of choice is, curiously, an NF theorem. Holmes (1998) takes these facts as evidence that NFU is a more successful foundation for mathematics than NF.
Holmes further argues that set theory is more natural with than without urelements, since we may take as urelements the objects of any theory or of the physical universe.[6]
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