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Mirrors > Home > MPE Home > Th. List > empty | Structured version Visualization version GIF version |
Description: Two characterizations of the empty domain. (Contributed by Gérard Lang, 5-Feb-2024.) |
Ref | Expression |
---|---|
empty | ⊢ (¬ ∃𝑥⊤ ↔ ∀𝑥⊥) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-fal 1549 | . . 3 ⊢ (⊥ ↔ ¬ ⊤) | |
2 | 1 | albii 1819 | . 2 ⊢ (∀𝑥⊥ ↔ ∀𝑥 ¬ ⊤) |
3 | alnex 1781 | . 2 ⊢ (∀𝑥 ¬ ⊤ ↔ ¬ ∃𝑥⊤) | |
4 | 2, 3 | bitr2i 278 | 1 ⊢ (¬ ∃𝑥⊤ ↔ ∀𝑥⊥) |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 ↔ wb 208 ∀wal 1534 ⊤wtru 1537 ⊥wfal 1548 ∃wex 1779 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1795 ax-4 1809 |
This theorem depends on definitions: df-bi 209 df-fal 1549 df-ex 1780 |
This theorem is referenced by: (None) |
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