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Mirrors > Home > MPE Home > Th. List > eq0 | Structured version Visualization version GIF version |
Description: A class is equal to the empty set if and only if it has no elements. Theorem 2 of [Suppes] p. 22. (Contributed by NM, 29-Aug-1993.) Avoid ax-11 2155, ax-12 2172. (Revised by Gino Giotto and Steven Nguyen, 28-Jun-2024.) Avoid ax-8 2109, df-clel 2811. (Revised by Gino Giotto, 6-Sep-2024.) |
Ref | Expression |
---|---|
eq0 | ⊢ (𝐴 = ∅ ↔ ∀𝑥 ¬ 𝑥 ∈ 𝐴) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | dfnul4 4324 | . . 3 ⊢ ∅ = {𝑦 ∣ ⊥} | |
2 | 1 | eqeq2i 2746 | . 2 ⊢ (𝐴 = ∅ ↔ 𝐴 = {𝑦 ∣ ⊥}) |
3 | dfcleq 2726 | . . 3 ⊢ (𝐴 = {𝑦 ∣ ⊥} ↔ ∀𝑥(𝑥 ∈ 𝐴 ↔ 𝑥 ∈ {𝑦 ∣ ⊥})) | |
4 | df-clab 2711 | . . . . . . 7 ⊢ (𝑥 ∈ {𝑦 ∣ ⊥} ↔ [𝑥 / 𝑦]⊥) | |
5 | sbv 2092 | . . . . . . 7 ⊢ ([𝑥 / 𝑦]⊥ ↔ ⊥) | |
6 | 4, 5 | bitri 275 | . . . . . 6 ⊢ (𝑥 ∈ {𝑦 ∣ ⊥} ↔ ⊥) |
7 | 6 | bibi2i 338 | . . . . 5 ⊢ ((𝑥 ∈ 𝐴 ↔ 𝑥 ∈ {𝑦 ∣ ⊥}) ↔ (𝑥 ∈ 𝐴 ↔ ⊥)) |
8 | nbfal 1557 | . . . . 5 ⊢ (¬ 𝑥 ∈ 𝐴 ↔ (𝑥 ∈ 𝐴 ↔ ⊥)) | |
9 | 7, 8 | bitr4i 278 | . . . 4 ⊢ ((𝑥 ∈ 𝐴 ↔ 𝑥 ∈ {𝑦 ∣ ⊥}) ↔ ¬ 𝑥 ∈ 𝐴) |
10 | 9 | albii 1822 | . . 3 ⊢ (∀𝑥(𝑥 ∈ 𝐴 ↔ 𝑥 ∈ {𝑦 ∣ ⊥}) ↔ ∀𝑥 ¬ 𝑥 ∈ 𝐴) |
11 | 3, 10 | bitri 275 | . 2 ⊢ (𝐴 = {𝑦 ∣ ⊥} ↔ ∀𝑥 ¬ 𝑥 ∈ 𝐴) |
12 | 2, 11 | bitri 275 | 1 ⊢ (𝐴 = ∅ ↔ ∀𝑥 ¬ 𝑥 ∈ 𝐴) |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 ↔ wb 205 ∀wal 1540 = wceq 1542 ⊥wfal 1554 [wsb 2068 ∈ wcel 2107 {cab 2710 ∅c0 4322 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1798 ax-4 1812 ax-5 1914 ax-6 1972 ax-7 2012 ax-9 2117 ax-ext 2704 |
This theorem depends on definitions: df-bi 206 df-an 398 df-tru 1545 df-fal 1555 df-ex 1783 df-sb 2069 df-clab 2711 df-cleq 2725 df-dif 3951 df-nul 4323 |
This theorem is referenced by: neq0 4345 nel0 4350 0el 4360 ssdif0 4363 difin0ss 4368 inssdif0 4369 ralf0OLD 4517 disjiun 5135 0ex 5307 reldm0 5926 iresn0n0 6052 uzwo 12892 hashgt0elex 14358 hausdiag 23141 rnelfmlem 23448 prv0 34410 wzel 34785 knoppndv 35399 bj-nul 35926 bj-nuliota 35927 bj-nuliotaALT 35928 nninfnub 36608 prtlem14 37733 orddif0suc 42004 nrhmzr 46634 zrninitoringc 46923 |
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