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Mirrors > Home > MPE Home > Th. List > sbbib | Structured version Visualization version GIF version |
Description: Reversal of substitution. (Contributed by AV, 6-Aug-2023.) (Proof shortened by Wolf Lammen, 4-Sep-2023.) |
Ref | Expression |
---|---|
sbbib.y | ⊢ Ⅎ𝑦𝜑 |
sbbib.x | ⊢ Ⅎ𝑥𝜓 |
Ref | Expression |
---|---|
sbbib | ⊢ (∀𝑦([𝑦 / 𝑥]𝜑 ↔ 𝜓) ↔ ∀𝑥(𝜑 ↔ [𝑥 / 𝑦]𝜓)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | nfs1v 2160 | . . 3 ⊢ Ⅎ𝑥[𝑦 / 𝑥]𝜑 | |
2 | sbbib.x | . . 3 ⊢ Ⅎ𝑥𝜓 | |
3 | 1, 2 | nfbi 1904 | . 2 ⊢ Ⅎ𝑥([𝑦 / 𝑥]𝜑 ↔ 𝜓) |
4 | sbbib.y | . . 3 ⊢ Ⅎ𝑦𝜑 | |
5 | nfs1v 2160 | . . 3 ⊢ Ⅎ𝑦[𝑥 / 𝑦]𝜓 | |
6 | 4, 5 | nfbi 1904 | . 2 ⊢ Ⅎ𝑦(𝜑 ↔ [𝑥 / 𝑦]𝜓) |
7 | sbequ12r 2254 | . . 3 ⊢ (𝑦 = 𝑥 → ([𝑦 / 𝑥]𝜑 ↔ 𝜑)) | |
8 | sbequ12 2253 | . . 3 ⊢ (𝑦 = 𝑥 → (𝜓 ↔ [𝑥 / 𝑦]𝜓)) | |
9 | 7, 8 | bibi12d 348 | . 2 ⊢ (𝑦 = 𝑥 → (([𝑦 / 𝑥]𝜑 ↔ 𝜓) ↔ (𝜑 ↔ [𝑥 / 𝑦]𝜓))) |
10 | 3, 6, 9 | cbvalv1 2361 | 1 ⊢ (∀𝑦([𝑦 / 𝑥]𝜑 ↔ 𝜓) ↔ ∀𝑥(𝜑 ↔ [𝑥 / 𝑦]𝜓)) |
Colors of variables: wff setvar class |
Syntax hints: ↔ wb 208 ∀wal 1535 Ⅎwnf 1784 [wsb 2069 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1796 ax-4 1810 ax-5 1911 ax-6 1970 ax-7 2015 ax-10 2145 ax-11 2161 ax-12 2177 |
This theorem depends on definitions: df-bi 209 df-an 399 df-or 844 df-tru 1540 df-ex 1781 df-nf 1785 df-sb 2070 |
This theorem is referenced by: sbbibvv 2381 dfich2 43662 dfich2ai 43663 |
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