Theorem vn0 4351

Description: The universal class is not equal to the empty set. (Contributed by NM, 11-Sep-2008.) Avoid ax-8 2108, df-clel 2814. (Revised by GG, 6-Sep-2024.)

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 1551	. . . . . . 7 ⊢ ¬ ⊥
2		pm5.501 366	. . . . . . . 8 ⊢ (⊤ → (⊥ ↔ (⊤ ↔ ⊥)))
3	2	mptru 1544	. . . . . . 7 ⊢ (⊥ ↔ (⊤ ↔ ⊥))
4	1, 3	mtbi 322	. . . . . 6 ⊢ ¬ (⊤ ↔ ⊥)
5	4	exgen 1972	. . . . 5 ⊢ ∃𝑦 ¬ (⊤ ↔ ⊥)
6		exnal 1824	. . . . 5 ⊢ (∃𝑦 ¬ (⊤ ↔ ⊥) ↔ ¬ ∀𝑦(⊤ ↔ ⊥))
7	5, 6	mpbi 230	. . . 4 ⊢ ¬ ∀𝑦(⊤ ↔ ⊥)
8		df-clab 2713	. . . . . . 7 ⊢ (𝑦 ∈ {𝑥 ∣ ⊤} ↔ [𝑦 / 𝑥]⊤)
9		sbv 2086	. . . . . . 7 ⊢ ([𝑦 / 𝑥]⊤ ↔ ⊤)
10	8, 9	bitr2i 276	. . . . . 6 ⊢ (⊤ ↔ 𝑦 ∈ {𝑥 ∣ ⊤})
11		df-clab 2713	. . . . . . 7 ⊢ (𝑦 ∈ {𝑥 ∣ ⊥} ↔ [𝑦 / 𝑥]⊥)
12		sbv 2086	. . . . . . 7 ⊢ ([𝑦 / 𝑥]⊥ ↔ ⊥)
13	11, 12	bitr2i 276	. . . . . 6 ⊢ (⊥ ↔ 𝑦 ∈ {𝑥 ∣ ⊥})
14	10, 13	bibi12i 339	. . . . 5 ⊢ ((⊤ ↔ ⊥) ↔ (𝑦 ∈ {𝑥 ∣ ⊤} ↔ 𝑦 ∈ {𝑥 ∣ ⊥}))
15	14	albii 1816	. . . 4 ⊢ (∀𝑦(⊤ ↔ ⊥) ↔ ∀𝑦(𝑦 ∈ {𝑥 ∣ ⊤} ↔ 𝑦 ∈ {𝑥 ∣ ⊥}))
16	7, 15	mtbi 322	. . 3 ⊢ ¬ ∀𝑦(𝑦 ∈ {𝑥 ∣ ⊤} ↔ 𝑦 ∈ {𝑥 ∣ ⊥})
17		dfcleq 2728	. . . 4 ⊢ ({𝑥 ∣ ⊤} = {𝑥 ∣ ⊥} ↔ ∀𝑦(𝑦 ∈ {𝑥 ∣ ⊤} ↔ 𝑦 ∈ {𝑥 ∣ ⊥}))
18		dfv2 3481	. . . . . 6 ⊢ V = {𝑥 ∣ ⊤}
19	18	eqcomi 2744	. . . . 5 ⊢ {𝑥 ∣ ⊤} = V
20		dfnul4 4341	. . . . . 6 ⊢ ∅ = {𝑥 ∣ ⊥}
21	20	eqcomi 2744	. . . . 5 ⊢ {𝑥 ∣ ⊥} = ∅
22	19, 21	eqeq12i 2753	. . . 4 ⊢ ({𝑥 ∣ ⊤} = {𝑥 ∣ ⊥} ↔ V = ∅)
23	17, 22	bitr3i 277	. . 3 ⊢ (∀𝑦(𝑦 ∈ {𝑥 ∣ ⊤} ↔ 𝑦 ∈ {𝑥 ∣ ⊥}) ↔ V = ∅)
24	16, 23	mtbi 322	. 2 ⊢ ¬ V = ∅
25	24	neir 2941	1 ⊢ V ≠ ∅

Syntax hints:  ¬ wn 3   ↔ wb 206  ∀wal 1535   = wceq 1537  ⊤wtru 1538  ⊥wfal 1549  ∃wex 1776  [wsb 2062   ∈ wcel 2106  {cab 2712   ≠ wne 2938  Vcvv 3478  ∅c0 4339

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1792  ax-4 1806  ax-5 1908  ax-6 1965  ax-7 2005  ax-9 2116  ax-ext 2706

This theorem depends on definitions:  df-bi 207  df-an 396  df-tru 1540  df-fal 1550  df-ex 1777  df-sb 2063  df-clab 2713  df-cleq 2727  df-ne 2939  df-v 3480  df-dif 3966  df-nul 4340

This theorem is referenced by:  uniintsn  4990  relrelss  6295  imasaddfnlem  17575  imasvscafn  17584  cmpfi  23432  fclscmp  24054  zarcmplem  33842  compne  44437