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Mirrors > Home > MPE Home > Th. List > dfnul4 | Structured version Visualization version GIF version |
Description: Alternate definition of the empty class/set. (Contributed by BJ, 30-Nov-2019.) Avoid ax-8 2116, df-clel 2812. (Revised by Gino Giotto, 3-Sep-2024.) Prove directly from definition to allow shortening dfnul2 4224. (Revised by BJ, 23-Sep-2024.) |
Ref | Expression |
---|---|
dfnul4 | ⊢ ∅ = {𝑥 ∣ ⊥} |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-nul 4222 | . 2 ⊢ ∅ = (V ∖ V) | |
2 | df-dif 3856 | . 2 ⊢ (V ∖ V) = {𝑥 ∣ (𝑥 ∈ V ∧ ¬ 𝑥 ∈ V)} | |
3 | pm3.24 406 | . . . 4 ⊢ ¬ (𝑥 ∈ V ∧ ¬ 𝑥 ∈ V) | |
4 | 3 | bifal 1558 | . . 3 ⊢ ((𝑥 ∈ V ∧ ¬ 𝑥 ∈ V) ↔ ⊥) |
5 | 4 | abbii 2804 | . 2 ⊢ {𝑥 ∣ (𝑥 ∈ V ∧ ¬ 𝑥 ∈ V)} = {𝑥 ∣ ⊥} |
6 | 1, 2, 5 | 3eqtri 2766 | 1 ⊢ ∅ = {𝑥 ∣ ⊥} |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 ∧ wa 399 = wceq 1542 ⊥wfal 1554 ∈ wcel 2114 {cab 2717 Vcvv 3400 ∖ cdif 3850 ∅c0 4221 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1802 ax-4 1816 ax-5 1917 ax-6 1975 ax-7 2020 ax-9 2124 ax-ext 2711 |
This theorem depends on definitions: df-bi 210 df-an 400 df-tru 1545 df-fal 1555 df-ex 1787 df-sb 2075 df-clab 2718 df-cleq 2731 df-dif 3856 df-nul 4222 |
This theorem is referenced by: dfnul2 4224 dfnul3 4225 noel 4229 vn0 4237 eq0 4242 ab0w 4272 ab0 4273 ab0OLD 4274 abf 4301 eq0rdv 4303 rzal 4405 ralf0 4410 |
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