Theorem vn0 4298

Description: The universal class is not equal to the empty set. (Contributed by NM, 11-Sep-2008.) Avoid ax-8 2148, df-clel 2840. (Revised by GG, 6-Sep-2024.) (Proof shortened by BJ, 12-Jul-2026.)

Assertion

Ref	Expression
vn0	⊢ V ≠ ∅

Proof of Theorem vn0

Dummy variables 𝑥 𝑦 are mutually distinct and distinct from all other variables.

Step	Hyp	Ref	Expression
1		fal 1584	. . . 4 ⊢ ¬ ⊥
2		vextru 2750	. . . . . 6 ⊢ 𝑦 ∈ {𝑥 ∣ ⊤}
3		biimp 218	. . . . . 6 ⊢ ((𝑦 ∈ {𝑥 ∣ ⊤} ↔ ⊥) → (𝑦 ∈ {𝑥 ∣ ⊤} → ⊥))
4	2, 3	mpi 21	. . . . 5 ⊢ ((𝑦 ∈ {𝑥 ∣ ⊤} ↔ ⊥) → ⊥)
5	4	spsv 2020	. . . 4 ⊢ (∀𝑦(𝑦 ∈ {𝑥 ∣ ⊤} ↔ ⊥) → ⊥)
6	1, 5	mto 200	. . 3 ⊢ ¬ ∀𝑦(𝑦 ∈ {𝑥 ∣ ⊤} ↔ ⊥)
7		dfv2 3460	. . . . 5 ⊢ V = {𝑥 ∣ ⊤}
8		dfnul4 4288	. . . . 5 ⊢ ∅ = {𝑥 ∣ ⊥}
9	7, 8	eqeq12i 2783	. . . 4 ⊢ (V = ∅ ↔ {𝑥 ∣ ⊤} = {𝑥 ∣ ⊥})
10		biidd 265	. . . . 5 ⊢ (𝑥 = 𝑦 → (⊥ ↔ ⊥))
11	10	eqabbw 2838	. . . 4 ⊢ ({𝑥 ∣ ⊤} = {𝑥 ∣ ⊥} ↔ ∀𝑦(𝑦 ∈ {𝑥 ∣ ⊤} ↔ ⊥))
12	9, 11	bitri 278	. . 3 ⊢ (V = ∅ ↔ ∀𝑦(𝑦 ∈ {𝑥 ∣ ⊤} ↔ ⊥))
13	6, 12	mtbir 326	. 2 ⊢ ¬ V = ∅
14	13	neir 2963	1 ⊢ V ≠ ∅

This proof depends on syntax axioms:   ↔ wb 209  ∀wal 1568   = wceq 1570  ⊤wtru 1571  ⊥wfal 1582   ∈ wcel 2146  {cab 2743   ≠ wne 2960  Vcvv 3457  ∅c0 4286

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-9 2156  ax-ext 2737

This proof depends on definitions:  df-bi 210  df-an 402  df-tru 1573  df-fal 1583  df-ex 1813  df-sb 2100  df-clab 2744  df-cleq 2757  df-ne 2961  df-v 3459  df-dif 3909  df-nul 4287

This theorem is used by:  uniintsn  4952  relrelss  6277  imasaddfnlem  17606  imasvscafn  17615  cmpfi  23617  fclscmp  24240  zarcmplem  34337  compne  45210