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Theorem nfsb4t 2517
 Description: A variable not free in a proposition remains so after substitution in that proposition with a distinct variable (closed form of nfsb4 2518). Usage of this theorem is discouraged because it depends on ax-13 2379. (Contributed by NM, 7-Apr-2004.) (Revised by Mario Carneiro, 4-Oct-2016.) (Proof shortened by Wolf Lammen, 11-May-2018.) (New usage is discouraged.)
Assertion
Ref Expression
nfsb4t (∀𝑥𝑧𝜑 → (¬ ∀𝑧 𝑧 = 𝑦 → Ⅎ𝑧[𝑦 / 𝑥]𝜑))

Proof of Theorem nfsb4t
StepHypRef Expression
1 sbequ12 2250 . . . . . . . 8 (𝑥 = 𝑦 → (𝜑 ↔ [𝑦 / 𝑥]𝜑))
21sps 2182 . . . . . . 7 (∀𝑥 𝑥 = 𝑦 → (𝜑 ↔ [𝑦 / 𝑥]𝜑))
32drnf2 2455 . . . . . 6 (∀𝑥 𝑥 = 𝑦 → (Ⅎ𝑧𝜑 ↔ Ⅎ𝑧[𝑦 / 𝑥]𝜑))
43biimpd 232 . . . . 5 (∀𝑥 𝑥 = 𝑦 → (Ⅎ𝑧𝜑 → Ⅎ𝑧[𝑦 / 𝑥]𝜑))
54spsd 2184 . . . 4 (∀𝑥 𝑥 = 𝑦 → (∀𝑥𝑧𝜑 → Ⅎ𝑧[𝑦 / 𝑥]𝜑))
65impcom 411 . . 3 ((∀𝑥𝑧𝜑 ∧ ∀𝑥 𝑥 = 𝑦) → Ⅎ𝑧[𝑦 / 𝑥]𝜑)
76a1d 25 . 2 ((∀𝑥𝑧𝜑 ∧ ∀𝑥 𝑥 = 𝑦) → (¬ ∀𝑧 𝑧 = 𝑦 → Ⅎ𝑧[𝑦 / 𝑥]𝜑))
8 nfnf1 2155 . . . . 5 𝑧𝑧𝜑
98nfal 2331 . . . 4 𝑧𝑥𝑧𝜑
10 nfnae 2445 . . . 4 𝑧 ¬ ∀𝑥 𝑥 = 𝑦
119, 10nfan 1900 . . 3 𝑧(∀𝑥𝑧𝜑 ∧ ¬ ∀𝑥 𝑥 = 𝑦)
12 nfa1 2152 . . . 4 𝑥𝑥𝑧𝜑
13 nfnae 2445 . . . 4 𝑥 ¬ ∀𝑥 𝑥 = 𝑦
1412, 13nfan 1900 . . 3 𝑥(∀𝑥𝑧𝜑 ∧ ¬ ∀𝑥 𝑥 = 𝑦)
15 sp 2180 . . . 4 (∀𝑥𝑧𝜑 → Ⅎ𝑧𝜑)
1615adantr 484 . . 3 ((∀𝑥𝑧𝜑 ∧ ¬ ∀𝑥 𝑥 = 𝑦) → Ⅎ𝑧𝜑)
17 nfsb2 2501 . . . 4 (¬ ∀𝑥 𝑥 = 𝑦 → Ⅎ𝑥[𝑦 / 𝑥]𝜑)
1817adantl 485 . . 3 ((∀𝑥𝑧𝜑 ∧ ¬ ∀𝑥 𝑥 = 𝑦) → Ⅎ𝑥[𝑦 / 𝑥]𝜑)
191a1i 11 . . 3 ((∀𝑥𝑧𝜑 ∧ ¬ ∀𝑥 𝑥 = 𝑦) → (𝑥 = 𝑦 → (𝜑 ↔ [𝑦 / 𝑥]𝜑)))
2011, 14, 16, 18, 19dvelimdf 2460 . 2 ((∀𝑥𝑧𝜑 ∧ ¬ ∀𝑥 𝑥 = 𝑦) → (¬ ∀𝑧 𝑧 = 𝑦 → Ⅎ𝑧[𝑦 / 𝑥]𝜑))
217, 20pm2.61dan 812 1 (∀𝑥𝑧𝜑 → (¬ ∀𝑧 𝑧 = 𝑦 → Ⅎ𝑧[𝑦 / 𝑥]𝜑))
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 209   ∧ wa 399  ∀wal 1536  Ⅎwnf 1785  [wsb 2069 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1911  ax-6 1970  ax-7 2015  ax-10 2142  ax-11 2158  ax-12 2175  ax-13 2379 This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-tru 1541  df-ex 1782  df-nf 1786  df-sb 2070 This theorem is referenced by:  nfsb4  2518  nfsbd  2541
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