Theorem mh-infprim3bi 36746

Description: An axiom of infinity in primitive symbols not requiring ax-reg 9500. This version of the axiom was designed by Stefan O'Rear for his zf2.nql program, see https://github.com/sorear/metamath-turing-machines 9500. It directly implies ax-inf 9550, but deriving ax-inf2 9553 requires ax-ext 2709 and ax-rep 5212, see mh-inf3sn 36740. (Contributed by Matthew House, 13-Apr-2026.)

Assertion

Ref	Expression
mh-infprim3bi	⊢ (∃𝑦(𝑥 ∈ 𝑦 ∧ ∀𝑧 ∈ 𝑦 {𝑧} ∈ 𝑦) ↔ ¬ ∀𝑦 ¬ ¬ (𝑥 ∈ 𝑦 → ¬ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))))

Distinct variable group:   𝑥,𝑦,𝑧

Proof of Theorem mh-infprim3bi

Step	Hyp	Ref	Expression
1		sneq 4578	. . . . . . . 8 ⊢ (𝑧 = 𝑥 → {𝑧} = {𝑥})
2	1	eleq1d 2822	. . . . . . 7 ⊢ (𝑧 = 𝑥 → ({𝑧} ∈ 𝑦 ↔ {𝑥} ∈ 𝑦))
3	2	cbvralvw 3216	. . . . . 6 ⊢ (∀𝑧 ∈ 𝑦 {𝑧} ∈ 𝑦 ↔ ∀𝑥 ∈ 𝑦 {𝑥} ∈ 𝑦)
4		dfclel 2813	. . . . . . . 8 ⊢ ({𝑥} ∈ 𝑦 ↔ ∃𝑧(𝑧 = {𝑥} ∧ 𝑧 ∈ 𝑦))
5		dfcleq 2730	. . . . . . . . . . . 12 ⊢ (𝑧 = {𝑥} ↔ ∀𝑦(𝑦 ∈ 𝑧 ↔ 𝑦 ∈ {𝑥}))
6		velsn 4584	. . . . . . . . . . . . . . 15 ⊢ (𝑦 ∈ {𝑥} ↔ 𝑦 = 𝑥)
7	6	bibi2i 337	. . . . . . . . . . . . . 14 ⊢ ((𝑦 ∈ 𝑧 ↔ 𝑦 ∈ {𝑥}) ↔ (𝑦 ∈ 𝑧 ↔ 𝑦 = 𝑥))
8		dfbi1 213	. . . . . . . . . . . . . 14 ⊢ ((𝑦 ∈ 𝑧 ↔ 𝑦 = 𝑥) ↔ ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧)))
9	7, 8	bitri 275	. . . . . . . . . . . . 13 ⊢ ((𝑦 ∈ 𝑧 ↔ 𝑦 ∈ {𝑥}) ↔ ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧)))
10	9	albii 1821	. . . . . . . . . . . 12 ⊢ (∀𝑦(𝑦 ∈ 𝑧 ↔ 𝑦 ∈ {𝑥}) ↔ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧)))
11	5, 10	bitri 275	. . . . . . . . . . 11 ⊢ (𝑧 = {𝑥} ↔ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧)))
12	11	anbi2ci 626	. . . . . . . . . 10 ⊢ ((𝑧 = {𝑥} ∧ 𝑧 ∈ 𝑦) ↔ (𝑧 ∈ 𝑦 ∧ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))
13		df-an 396	. . . . . . . . . 10 ⊢ ((𝑧 ∈ 𝑦 ∧ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))) ↔ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))
14	12, 13	bitri 275	. . . . . . . . 9 ⊢ ((𝑧 = {𝑥} ∧ 𝑧 ∈ 𝑦) ↔ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))
15	14	exbii 1850	. . . . . . . 8 ⊢ (∃𝑧(𝑧 = {𝑥} ∧ 𝑧 ∈ 𝑦) ↔ ∃𝑧 ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))
16		df-ex 1782	. . . . . . . 8 ⊢ (∃𝑧 ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))) ↔ ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))
17	4, 15, 16	3bitri 297	. . . . . . 7 ⊢ ({𝑥} ∈ 𝑦 ↔ ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))
18	17	ralbii 3084	. . . . . 6 ⊢ (∀𝑥 ∈ 𝑦 {𝑥} ∈ 𝑦 ↔ ∀𝑥 ∈ 𝑦 ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))
19		df-ral 3053	. . . . . 6 ⊢ (∀𝑥 ∈ 𝑦 ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))) ↔ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧)))))
20	3, 18, 19	3bitri 297	. . . . 5 ⊢ (∀𝑧 ∈ 𝑦 {𝑧} ∈ 𝑦 ↔ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧)))))
21	20	anbi2i 624	. . . 4 ⊢ ((𝑥 ∈ 𝑦 ∧ ∀𝑧 ∈ 𝑦 {𝑧} ∈ 𝑦) ↔ (𝑥 ∈ 𝑦 ∧ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))))
22		df-an 396	. . . 4 ⊢ ((𝑥 ∈ 𝑦 ∧ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))) ↔ ¬ (𝑥 ∈ 𝑦 → ¬ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))))
23	21, 22	bitri 275	. . 3 ⊢ ((𝑥 ∈ 𝑦 ∧ ∀𝑧 ∈ 𝑦 {𝑧} ∈ 𝑦) ↔ ¬ (𝑥 ∈ 𝑦 → ¬ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))))
24	23	exbii 1850	. 2 ⊢ (∃𝑦(𝑥 ∈ 𝑦 ∧ ∀𝑧 ∈ 𝑦 {𝑧} ∈ 𝑦) ↔ ∃𝑦 ¬ (𝑥 ∈ 𝑦 → ¬ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))))
25		df-ex 1782	. 2 ⊢ (∃𝑦 ¬ (𝑥 ∈ 𝑦 → ¬ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))) ↔ ¬ ∀𝑦 ¬ ¬ (𝑥 ∈ 𝑦 → ¬ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))))
26	24, 25	bitri 275	1 ⊢ (∃𝑦(𝑥 ∈ 𝑦 ∧ ∀𝑧 ∈ 𝑦 {𝑧} ∈ 𝑦) ↔ ¬ ∀𝑦 ¬ ¬ (𝑥 ∈ 𝑦 → ¬ ∀𝑥(𝑥 ∈ 𝑦 → ¬ ∀𝑧 ¬ ¬ (𝑧 ∈ 𝑦 → ¬ ∀𝑦 ¬ ((𝑦 ∈ 𝑧 → 𝑦 = 𝑥) → ¬ (𝑦 = 𝑥 → 𝑦 ∈ 𝑧))))))

Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 206   ∧ wa 395  ∀wal 1540   = wceq 1542  ∃wex 1781   ∈ wcel 2114  ∀wral 3052  {csn 4568

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1912  ax-6 1969  ax-7 2010  ax-8 2116  ax-9 2124  ax-ext 2709

This theorem depends on definitions:  df-bi 207  df-an 396  df-tru 1545  df-ex 1782  df-sb 2069  df-clab 2716  df-cleq 2729  df-clel 2812  df-ral 3053  df-v 3432  df-sn 4569

This theorem is referenced by: (None)