![]() |
Mathbox for Alexander van der Vekens |
< Previous
Next >
Nearby theorems |
|
Mirrors > Home > MPE Home > Th. List > Mathboxes > ichnfb | Structured version Visualization version GIF version |
Description: If 𝑥 and 𝑦 are interchangeable in 𝜑, they are both free or both not free in 𝜑. (Contributed by Wolf Lammen, 6-Aug-2023.) (Revised by AV, 23-Sep-2023.) |
Ref | Expression |
---|---|
ichnfb | ⊢ ([𝑥⇄𝑦]𝜑 → (∀𝑥Ⅎ𝑦𝜑 ↔ ∀𝑦Ⅎ𝑥𝜑)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ichcom 45741 | . . . 4 ⊢ ([𝑥⇄𝑦]𝜑 ↔ [𝑦⇄𝑥]𝜑) | |
2 | ichnfim 45746 | . . . 4 ⊢ ((∀𝑥Ⅎ𝑦𝜑 ∧ [𝑦⇄𝑥]𝜑) → ∀𝑦Ⅎ𝑥𝜑) | |
3 | 1, 2 | sylan2b 595 | . . 3 ⊢ ((∀𝑥Ⅎ𝑦𝜑 ∧ [𝑥⇄𝑦]𝜑) → ∀𝑦Ⅎ𝑥𝜑) |
4 | 3 | expcom 415 | . 2 ⊢ ([𝑥⇄𝑦]𝜑 → (∀𝑥Ⅎ𝑦𝜑 → ∀𝑦Ⅎ𝑥𝜑)) |
5 | ichnfim 45746 | . . 3 ⊢ ((∀𝑦Ⅎ𝑥𝜑 ∧ [𝑥⇄𝑦]𝜑) → ∀𝑥Ⅎ𝑦𝜑) | |
6 | 5 | expcom 415 | . 2 ⊢ ([𝑥⇄𝑦]𝜑 → (∀𝑦Ⅎ𝑥𝜑 → ∀𝑥Ⅎ𝑦𝜑)) |
7 | 4, 6 | impbid 211 | 1 ⊢ ([𝑥⇄𝑦]𝜑 → (∀𝑥Ⅎ𝑦𝜑 ↔ ∀𝑦Ⅎ𝑥𝜑)) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ↔ wb 205 ∀wal 1540 Ⅎwnf 1786 [wich 45727 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1798 ax-4 1812 ax-5 1914 ax-6 1972 ax-7 2012 ax-10 2138 ax-11 2155 ax-12 2172 |
This theorem depends on definitions: df-bi 206 df-an 398 df-or 847 df-tru 1545 df-ex 1783 df-nf 1787 df-sb 2069 df-ich 45728 |
This theorem is referenced by: (None) |
Copyright terms: Public domain | W3C validator |