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Mirrors > Home > MPE Home > Th. List > hbe1 | Structured version Visualization version GIF version |
Description: The setvar 𝑥 is not free in ∃𝑥𝜑. Corresponds to the axiom (5) of modal logic (see also modal5 2145). (Contributed by NM, 24-Jan-1993.) |
Ref | Expression |
---|---|
hbe1 | ⊢ (∃𝑥𝜑 → ∀𝑥∃𝑥𝜑) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-ex 1775 | . 2 ⊢ (∃𝑥𝜑 ↔ ¬ ∀𝑥 ¬ 𝜑) | |
2 | hbn1 2131 | . 2 ⊢ (¬ ∀𝑥 ¬ 𝜑 → ∀𝑥 ¬ ∀𝑥 ¬ 𝜑) | |
3 | 1, 2 | hbxfrbi 1820 | 1 ⊢ (∃𝑥𝜑 → ∀𝑥∃𝑥𝜑) |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 → wi 4 ∀wal 1532 ∃wex 1774 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1790 ax-4 1804 ax-10 2130 |
This theorem depends on definitions: df-bi 206 df-ex 1775 |
This theorem is referenced by: nfe1 2140 equs5eALT 2360 nfeqf2 2372 equs5e 2453 axie1 2693 bj-wnf2 36189 bj-nnfe1 36231 ac6s6 37639 exlimexi 43957 vk15.4j 43961 vk15.4jVD 44347 |
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