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Theorem 2sb6rf 1882
 Description: Reversed double substitution. (Contributed by NM, 3-Feb-2005.)
Hypotheses
Ref Expression
2sb5rf.1 (𝜑 → ∀𝑧𝜑)
2sb5rf.2 (𝜑 → ∀𝑤𝜑)
Assertion
Ref Expression
2sb6rf (𝜑 ↔ ∀𝑧𝑤((𝑧 = 𝑥𝑤 = 𝑦) → [𝑧 / 𝑥][𝑤 / 𝑦]𝜑))
Distinct variable groups:   𝑥,𝑦   𝑥,𝑤   𝑦,𝑧   𝑧,𝑤
Allowed substitution hints:   𝜑(𝑥,𝑦,𝑧,𝑤)

Proof of Theorem 2sb6rf
StepHypRef Expression
1 2sb5rf.1 . . 3 (𝜑 → ∀𝑧𝜑)
21sb6rf 1749 . 2 (𝜑 ↔ ∀𝑧(𝑧 = 𝑥 → [𝑧 / 𝑥]𝜑))
3 19.21v 1769 . . . 4 (∀𝑤(𝑧 = 𝑥 → (𝑤 = 𝑦 → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑)) ↔ (𝑧 = 𝑥 → ∀𝑤(𝑤 = 𝑦 → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑)))
4 sbcom2 1879 . . . . . . 7 ([𝑧 / 𝑥][𝑤 / 𝑦]𝜑 ↔ [𝑤 / 𝑦][𝑧 / 𝑥]𝜑)
54imbi2i 219 . . . . . 6 (((𝑧 = 𝑥𝑤 = 𝑦) → [𝑧 / 𝑥][𝑤 / 𝑦]𝜑) ↔ ((𝑧 = 𝑥𝑤 = 𝑦) → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑))
6 impexp 254 . . . . . 6 (((𝑧 = 𝑥𝑤 = 𝑦) → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑) ↔ (𝑧 = 𝑥 → (𝑤 = 𝑦 → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑)))
75, 6bitri 177 . . . . 5 (((𝑧 = 𝑥𝑤 = 𝑦) → [𝑧 / 𝑥][𝑤 / 𝑦]𝜑) ↔ (𝑧 = 𝑥 → (𝑤 = 𝑦 → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑)))
87albii 1375 . . . 4 (∀𝑤((𝑧 = 𝑥𝑤 = 𝑦) → [𝑧 / 𝑥][𝑤 / 𝑦]𝜑) ↔ ∀𝑤(𝑧 = 𝑥 → (𝑤 = 𝑦 → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑)))
9 2sb5rf.2 . . . . . . 7 (𝜑 → ∀𝑤𝜑)
109hbsbv 1833 . . . . . 6 ([𝑧 / 𝑥]𝜑 → ∀𝑤[𝑧 / 𝑥]𝜑)
1110sb6rf 1749 . . . . 5 ([𝑧 / 𝑥]𝜑 ↔ ∀𝑤(𝑤 = 𝑦 → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑))
1211imbi2i 219 . . . 4 ((𝑧 = 𝑥 → [𝑧 / 𝑥]𝜑) ↔ (𝑧 = 𝑥 → ∀𝑤(𝑤 = 𝑦 → [𝑤 / 𝑦][𝑧 / 𝑥]𝜑)))
133, 8, 123bitr4ri 206 . . 3 ((𝑧 = 𝑥 → [𝑧 / 𝑥]𝜑) ↔ ∀𝑤((𝑧 = 𝑥𝑤 = 𝑦) → [𝑧 / 𝑥][𝑤 / 𝑦]𝜑))
1413albii 1375 . 2 (∀𝑧(𝑧 = 𝑥 → [𝑧 / 𝑥]𝜑) ↔ ∀𝑧𝑤((𝑧 = 𝑥𝑤 = 𝑦) → [𝑧 / 𝑥][𝑤 / 𝑦]𝜑))
152, 14bitri 177 1 (𝜑 ↔ ∀𝑧𝑤((𝑧 = 𝑥𝑤 = 𝑦) → [𝑧 / 𝑥][𝑤 / 𝑦]𝜑))
 Colors of variables: wff set class Syntax hints:   → wi 4   ∧ wa 101   ↔ wb 102  ∀wal 1257  [wsb 1661 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 103  ax-ia2 104  ax-ia3 105  ax-io 640  ax-5 1352  ax-7 1353  ax-gen 1354  ax-ie1 1398  ax-ie2 1399  ax-8 1411  ax-10 1412  ax-11 1413  ax-i12 1414  ax-4 1416  ax-17 1435  ax-i9 1439  ax-ial 1443  ax-i5r 1444 This theorem depends on definitions:  df-bi 114  df-nf 1366  df-sb 1662 This theorem is referenced by: (None)
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