Theorem ssclaxsep 45909

Description: A class that is closed under subsets models the Axiom of Separation ax-sep 5248. Lemma II.2.4(3) of [Kunen2] p. 111.

Note that, to obtain the relativization of an instance of Separation to 𝑀, the formula 𝜑 would need to be replaced with its relativization to 𝑀. However, this new formula is a valid substitution for 𝜑, so this theorem does establish that all instances of Separation hold in 𝑀. (Contributed by Eric Schmidt, 29-Sep-2025.)

Assertion

Ref	Expression
ssclaxsep	⊢ (∀𝑧 ∈ 𝑀 𝒫 𝑧 ⊆ 𝑀 → ∀𝑧 ∈ 𝑀 ∃𝑦 ∈ 𝑀 ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))

Distinct variable groups:   𝑥,𝑦,𝑧   𝜑,𝑦,𝑧   𝑦,𝑀

Allowed substitution hints:   𝜑(𝑥)   𝑀(𝑥, 𝑧)

Proof of Theorem ssclaxsep

Step	Hyp	Ref	Expression
1		ax-sep 5248	. . . 4 ⊢ ∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))
2		biimp 218	. . . . . . . . . 10 ⊢ ((𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → (𝑥 ∈ 𝑦 → (𝑥 ∈ 𝑧 ∧ 𝜑)))
3		simpl 488	. . . . . . . . . 10 ⊢ ((𝑥 ∈ 𝑧 ∧ 𝜑) → 𝑥 ∈ 𝑧)
4	2, 3	syl6 36	. . . . . . . . 9 ⊢ ((𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → (𝑥 ∈ 𝑦 → 𝑥 ∈ 𝑧))
5	4	alimi 1844	. . . . . . . 8 ⊢ (∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → ∀𝑥(𝑥 ∈ 𝑦 → 𝑥 ∈ 𝑧))
6		velpw 4561	. . . . . . . . 9 ⊢ (𝑦 ∈ 𝒫 𝑧 ↔ 𝑦 ⊆ 𝑧)
7		df-ss 3915	. . . . . . . . 9 ⊢ (𝑦 ⊆ 𝑧 ↔ ∀𝑥(𝑥 ∈ 𝑦 → 𝑥 ∈ 𝑧))
8	6, 7	bitr2i 279	. . . . . . . 8 ⊢ (∀𝑥(𝑥 ∈ 𝑦 → 𝑥 ∈ 𝑧) ↔ 𝑦 ∈ 𝒫 𝑧)
9	5, 8	sylib 221	. . . . . . 7 ⊢ (∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → 𝑦 ∈ 𝒫 𝑧)
10		ssel 3924	. . . . . . 7 ⊢ (𝒫 𝑧 ⊆ 𝑀 → (𝑦 ∈ 𝒫 𝑧 → 𝑦 ∈ 𝑀))
11	9, 10	syl5 35	. . . . . 6 ⊢ (𝒫 𝑧 ⊆ 𝑀 → (∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → 𝑦 ∈ 𝑀))
12		alral 3091	. . . . . 6 ⊢ (∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))
13	11, 12	jca2 523	. . . . 5 ⊢ (𝒫 𝑧 ⊆ 𝑀 → (∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → (𝑦 ∈ 𝑀 ∧ ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))))
14	13	eximdv 1950	. . . 4 ⊢ (𝒫 𝑧 ⊆ 𝑀 → (∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → ∃𝑦(𝑦 ∈ 𝑀 ∧ ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))))
15	1, 14	mpi 21	. . 3 ⊢ (𝒫 𝑧 ⊆ 𝑀 → ∃𝑦(𝑦 ∈ 𝑀 ∧ ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
16		df-rex 3087	. . 3 ⊢ (∃𝑦 ∈ 𝑀 ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) ↔ ∃𝑦(𝑦 ∈ 𝑀 ∧ ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
17	15, 16	sylibr 237	. 2 ⊢ (𝒫 𝑧 ⊆ 𝑀 → ∃𝑦 ∈ 𝑀 ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))
18	17	ralimi 3099	1 ⊢ (∀𝑧 ∈ 𝑀 𝒫 𝑧 ⊆ 𝑀 → ∀𝑧 ∈ 𝑀 ∃𝑦 ∈ 𝑀 ∀𝑥 ∈ 𝑀 (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))

This proof depends on syntax axioms:   → wi 4   ↔ wb 209   ∧ wa 401  ∀wal 1568  ∃wex 1812   ∈ wcel 2145  ∀wral 3076  ∃wrex 3086   ⊆ wss 3898  𝒫 cpw 4556

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1828  ax-4 1842  ax-5 1943  ax-6 2000  ax-7 2041  ax-8 2147  ax-9 2155  ax-ext 2732  ax-sep 5248

This proof depends on definitions:  df-bi 210  df-an 402  df-tru 1573  df-ex 1813  df-sb 2100  df-clab 2739  df-cleq 2752  df-clel 2835  df-ral 3077  df-rex 3087  df-v 3452  df-ss 3915  df-pw 4558

This theorem is used by:  wfaxsep  45922