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Mirrors > Home > ILE Home > Th. List > dfsb7a | GIF version |
Description: An alternate definition of proper substitution df-sb 1704. Similar to dfsb7 1927 in that it involves a dummy variable 𝑧, but expressed in terms of ∀ rather than ∃. For a version which only requires Ⅎ𝑧𝜑 rather than 𝑧 and 𝜑 being distinct, see sb7af 1929. (Contributed by Jim Kingdon, 5-Feb-2018.) |
Ref | Expression |
---|---|
dfsb7a | ⊢ ([𝑦 / 𝑥]𝜑 ↔ ∀𝑧(𝑧 = 𝑦 → ∀𝑥(𝑥 = 𝑧 → 𝜑))) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | nfv 1476 | . 2 ⊢ Ⅎ𝑧𝜑 | |
2 | 1 | sb7af 1929 | 1 ⊢ ([𝑦 / 𝑥]𝜑 ↔ ∀𝑧(𝑧 = 𝑦 → ∀𝑥(𝑥 = 𝑧 → 𝜑))) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ↔ wb 104 ∀wal 1297 [wsb 1703 |
This theorem was proved from axioms: ax-1 5 ax-2 6 ax-mp 7 ax-ia1 105 ax-ia2 106 ax-ia3 107 ax-io 671 ax-5 1391 ax-7 1392 ax-gen 1393 ax-ie1 1437 ax-ie2 1438 ax-8 1450 ax-10 1451 ax-11 1452 ax-i12 1453 ax-bndl 1454 ax-4 1455 ax-17 1474 ax-i9 1478 ax-ial 1482 ax-i5r 1483 |
This theorem depends on definitions: df-bi 116 df-nf 1405 df-sb 1704 |
This theorem is referenced by: (None) |
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