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Mirrors > Home > MPE Home > Th. List > Mathboxes > ralfal | Structured version Visualization version GIF version |
Description: Two ways of expressing empty set. (Contributed by Glauco Siliprandi, 24-Jan-2024.) |
Ref | Expression |
---|---|
ralfal.1 | ⊢ Ⅎ𝑥𝐴 |
Ref | Expression |
---|---|
ralfal | ⊢ (𝐴 = ∅ ↔ ∀𝑥 ∈ 𝐴 ⊥) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-fal 1549 | . . . 4 ⊢ (⊥ ↔ ¬ ⊤) | |
2 | 1 | ralbii 3090 | . . 3 ⊢ (∀𝑥 ∈ 𝐴 ⊥ ↔ ∀𝑥 ∈ 𝐴 ¬ ⊤) |
3 | ralnex 3069 | . . 3 ⊢ (∀𝑥 ∈ 𝐴 ¬ ⊤ ↔ ¬ ∃𝑥 ∈ 𝐴 ⊤) | |
4 | 2, 3 | bitri 275 | . 2 ⊢ (∀𝑥 ∈ 𝐴 ⊥ ↔ ¬ ∃𝑥 ∈ 𝐴 ⊤) |
5 | rextru 3074 | . . 3 ⊢ (∃𝑥 𝑥 ∈ 𝐴 ↔ ∃𝑥 ∈ 𝐴 ⊤) | |
6 | 5 | notbii 320 | . 2 ⊢ (¬ ∃𝑥 𝑥 ∈ 𝐴 ↔ ¬ ∃𝑥 ∈ 𝐴 ⊤) |
7 | ralfal.1 | . . . 4 ⊢ Ⅎ𝑥𝐴 | |
8 | 7 | neq0f 4353 | . . 3 ⊢ (¬ 𝐴 = ∅ ↔ ∃𝑥 𝑥 ∈ 𝐴) |
9 | 8 | con1bii 356 | . 2 ⊢ (¬ ∃𝑥 𝑥 ∈ 𝐴 ↔ 𝐴 = ∅) |
10 | 4, 6, 9 | 3bitr2ri 300 | 1 ⊢ (𝐴 = ∅ ↔ ∀𝑥 ∈ 𝐴 ⊥) |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 ↔ wb 206 = wceq 1536 ⊤wtru 1537 ⊥wfal 1548 ∃wex 1775 ∈ wcel 2105 Ⅎwnfc 2887 ∀wral 3058 ∃wrex 3067 ∅c0 4338 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1791 ax-4 1805 ax-5 1907 ax-6 1964 ax-7 2004 ax-8 2107 ax-9 2115 ax-11 2154 ax-12 2174 ax-ext 2705 |
This theorem depends on definitions: df-bi 207 df-an 396 df-or 848 df-tru 1539 df-fal 1549 df-ex 1776 df-nf 1780 df-sb 2062 df-clab 2712 df-cleq 2726 df-clel 2813 df-nfc 2889 df-ral 3059 df-rex 3068 df-dif 3965 df-nul 4339 |
This theorem is referenced by: (None) |
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