Theorem axsepg3ALT 35402

Description: Alternate proof of axsepg3 35401, derived directly from ax-sep 5245 with no additional set theory axioms. (Contributed by BTernaryTau, 3-Aug-2025.) (Proof modification is discouraged.) (New usage is discouraged.)

Assertion

Ref	Expression
axsepg3ALT	⊢ ∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))

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

Allowed substitution hint:   𝜑(𝑥)

Proof of Theorem axsepg3ALT

Dummy variables 𝑤 𝑣 are mutually distinct and distinct from all other variables.

Step	Hyp	Ref	Expression
1		nfv 1933	. . 3 ⊢ Ⅎ𝑥 ¬ ∀𝑦 𝑦 = 𝑧
2		nfvd 1934	. . . 4 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → Ⅎ𝑦 𝑥 ∈ 𝑤)
3		nfcvf 2949	. . . . . 6 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → Ⅎ𝑦𝑧)
4	3	nfcrd 2917	. . . . 5 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → Ⅎ𝑦 𝑥 ∈ 𝑧)
5		nfvd 1934	. . . . 5 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → Ⅎ𝑦𝜑)
6	4, 5	nfand 1916	. . . 4 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → Ⅎ𝑦(𝑥 ∈ 𝑧 ∧ 𝜑))
7	2, 6	nfbid 1921	. . 3 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → Ⅎ𝑦(𝑥 ∈ 𝑤 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))
8	1, 7	nfald 2359	. 2 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → Ⅎ𝑦∀𝑥(𝑥 ∈ 𝑤 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))
9		nfvd 1934	. 2 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → Ⅎ𝑤∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))
10		elequ2 2156	. . . . . 6 ⊢ (𝑤 = 𝑦 → (𝑥 ∈ 𝑤 ↔ 𝑥 ∈ 𝑦))
11	10	bibi1d 345	. . . . 5 ⊢ (𝑤 = 𝑦 → ((𝑥 ∈ 𝑤 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) ↔ (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
12	11	biimpd 231	. . . 4 ⊢ (𝑤 = 𝑦 → ((𝑥 ∈ 𝑤 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
13	12	alimdv 1935	. . 3 ⊢ (𝑤 = 𝑦 → (∀𝑥(𝑥 ∈ 𝑤 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → ∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
14	13	a1i 11	. 2 ⊢ (¬ ∀𝑦 𝑦 = 𝑧 → (𝑤 = 𝑦 → (∀𝑥(𝑥 ∈ 𝑤 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)) → ∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))))
15		elequ2 2156	. . . . . . 7 ⊢ (𝑦 = 𝑧 → (𝑥 ∈ 𝑦 ↔ 𝑥 ∈ 𝑧))
16	15	anbi1d 640	. . . . . 6 ⊢ (𝑦 = 𝑧 → ((𝑥 ∈ 𝑦 ∧ 𝜑) ↔ (𝑥 ∈ 𝑧 ∧ 𝜑)))
17	16	bibi2d 344	. . . . 5 ⊢ (𝑦 = 𝑧 → ((𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑦 ∧ 𝜑)) ↔ (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
18	17	biimpd 231	. . . 4 ⊢ (𝑦 = 𝑧 → ((𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑦 ∧ 𝜑)) → (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
19	18	alimdv 1935	. . 3 ⊢ (𝑦 = 𝑧 → (∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑦 ∧ 𝜑)) → ∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
20	19	sps 2219	. 2 ⊢ (∀𝑦 𝑦 = 𝑧 → (∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑦 ∧ 𝜑)) → ∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))))
21		ax-sep 5245	. 2 ⊢ ∃𝑤∀𝑥(𝑥 ∈ 𝑤 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))
22		ax-sep 5245	. . 3 ⊢ ∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑣 ∧ ⊥))
23		fal 1573	. . . . . . 7 ⊢ ¬ ⊥
24	23	intnan 490	. . . . . 6 ⊢ ¬ (𝑥 ∈ 𝑣 ∧ ⊥)
25		biimp 217	. . . . . 6 ⊢ ((𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑣 ∧ ⊥)) → (𝑥 ∈ 𝑦 → (𝑥 ∈ 𝑣 ∧ ⊥)))
26	24, 25	mtoi 201	. . . . 5 ⊢ ((𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑣 ∧ ⊥)) → ¬ 𝑥 ∈ 𝑦)
27	26	bianfd 542	. . . 4 ⊢ ((𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑣 ∧ ⊥)) → (𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑦 ∧ 𝜑)))
28	27	alimi 1830	. . 3 ⊢ (∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑣 ∧ ⊥)) → ∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑦 ∧ 𝜑)))
29	22, 28	eximii 1856	. 2 ⊢ ∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑦 ∧ 𝜑))
30	8, 9, 14, 20, 21, 29	dvelimexcasei 35337	1 ⊢ ∃𝑦∀𝑥(𝑥 ∈ 𝑦 ↔ (𝑥 ∈ 𝑧 ∧ 𝜑))

Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 208   ∧ wa 399  ∀wal 1557  ⊥wfal 1571  ∃wex 1798

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1814  ax-4 1828  ax-5 1929  ax-6 1986  ax-7 2027  ax-8 2143  ax-9 2151  ax-10 2174  ax-11 2190  ax-12 2211  ax-13 2402  ax-sep 5245

This theorem depends on definitions:  df-bi 209  df-an 400  df-or 859  df-tru 1562  df-fal 1572  df-ex 1799  df-nf 1803  df-clel 2836  df-nfc 2910

This theorem is referenced by: (None)