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INTER-UNIVERSAL TEICHMULLER THEORY IV:LOG-VOLUME COMPUTATIONS AND SET-THEORETIC FOUNDATIONS
Shinichi Mochizuki April 2020
(抜粋)
P67
Section 3: Inter-universal Formalism: the Language of Species
In the following discussion, we shall work with various models ー consisting
of “sets” and a relation “∈” ー of the standard ZFC axioms of axiomatic set theory
[i.e., the nine axioms of Zermelo-Fraenkel, together with the axiom of choice ー
cf., e.g., [Drk], Chapter 1, §3]. We shall refer to such models as ZFC-models.
Recall that a (Grothendieck) universe V is a set satisfying the following axioms [cf.[McLn], p. 194]:
The various ZFC-models that we work with may be thought of as [but are
not restricted to be!] the ZFC-models determined by various universes that are
sets relative to some ambient ZFC-model which, in addition to the standard axioms of ZFC set theory, satisfies the following existence axiom [attributed to the
“Grothendieck school” ー cf. the discussion of [McLn], p. 193]:
(†G) Given any set x, there exists a universe V such that x ∈ V .
We shall refer to a ZFC-model that also satisfies this additional axiom of the
Grothendieck school as a ZFCG-model. This existence axiom (†G) implies, in particular, that:
Given a set I and a collection of universes Vi, where i ∈ I, indexed by I
[i.e., a ‘function’ I ∋ i → Vi], there exists a [larger] universe V such that
Vi ∈ V , for i ∈ I.
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