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Mirrors > Home > MPE Home > Th. List > nfexd | Structured version Visualization version GIF version |
Description: If 𝑥 is not free in 𝜓, then it is not free in ∃𝑦𝜓. (Contributed by Mario Carneiro, 24-Sep-2016.) |
Ref | Expression |
---|---|
nfald.1 | ⊢ Ⅎ𝑦𝜑 |
nfald.2 | ⊢ (𝜑 → Ⅎ𝑥𝜓) |
Ref | Expression |
---|---|
nfexd | ⊢ (𝜑 → Ⅎ𝑥∃𝑦𝜓) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-ex 1777 | . 2 ⊢ (∃𝑦𝜓 ↔ ¬ ∀𝑦 ¬ 𝜓) | |
2 | nfald.1 | . . . 4 ⊢ Ⅎ𝑦𝜑 | |
3 | nfald.2 | . . . . 5 ⊢ (𝜑 → Ⅎ𝑥𝜓) | |
4 | 3 | nfnd 1856 | . . . 4 ⊢ (𝜑 → Ⅎ𝑥 ¬ 𝜓) |
5 | 2, 4 | nfald 2327 | . . 3 ⊢ (𝜑 → Ⅎ𝑥∀𝑦 ¬ 𝜓) |
6 | 5 | nfnd 1856 | . 2 ⊢ (𝜑 → Ⅎ𝑥 ¬ ∀𝑦 ¬ 𝜓) |
7 | 1, 6 | nfxfrd 1851 | 1 ⊢ (𝜑 → Ⅎ𝑥∃𝑦𝜓) |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 → wi 4 ∀wal 1535 ∃wex 1776 Ⅎwnf 1780 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1792 ax-4 1806 ax-5 1908 ax-6 1965 ax-7 2005 ax-10 2139 ax-11 2155 ax-12 2175 |
This theorem depends on definitions: df-bi 207 df-or 848 df-ex 1777 df-nf 1781 |
This theorem is referenced by: nfmod2 2556 nfmodv 2557 nfeudw 2589 nfeld 2915 nfopabd 5216 nfttrcld 9748 axrepndlem1 10630 axrepndlem2 10631 axunndlem1 10633 axunnd 10634 axpowndlem2 10636 axpowndlem3 10637 axpowndlem4 10638 axregndlem2 10641 axinfndlem1 10643 axinfnd 10644 axacndlem4 10648 axacndlem5 10649 axacnd 10650 19.9d2rf 32498 hbexg 44554 |
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