>>198
>>私は集合と要素を別のものとして区分するのは反対です
>無制限に、なんでも集合に取り入れると、まずいので公理化した
>で、素朴集合論から、公理的集合論（主としてZFC）の時代になった

（>>58）
http://blacaman.tripod.com/cursos/pdf/2012-2_0941.pdf
An Introduction to Independence Proofs K KUNEN 著 First edition: 1980 Seventh impression: 1999

https://www.amazon.co.jp/dp/4535783829/ref=pd_lpo_sbs_14_t_1?_encoding=UTF8&;psc=1&refRID=8NKTZE2Q63MR3BRQEWQX
集合論―独立性証明への案内 単行本 ? 2008/1/1
ケネス キューネン (著), Kenneth Kunen (原著), 藤田 博司 (翻訳)

下記が参考になるでしょう。
これの
P8
In the intended interpretation, under which the axioms of ZFC are presumed
true, x ∈ y is interpreted to mean that x is a member of y, but the
domain of discourse is somewhat harder to describe. In accordance with the
belief that set theory is the foundation of mathematics, we should be able
to capture all of mathematics by just talking about sets, so our variables
should not range over objects like cows and pigs. But if C is a cow, {C} is
a set, but not a legitimate mathematical object. More generally, since we
wish to talk only about sets but also should be able to talk about any element
of a set in our domain of discourse, all the elements of such a set should
be sets also.

つづく