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Theorem nfeqf2OLD 2464
Description: Obsolete version of nfeqf2 2463 as of 9-Jul-2022. (Contributed by Wolf Lammen, 9-Jun-2019.) (New usage is discouraged.) (Proof modification is discouraged.)
Assertion
Ref Expression
nfeqf2OLD (¬ ∀𝑥 𝑥 = 𝑦 → Ⅎ𝑥 𝑧 = 𝑦)
Distinct variable group:   𝑥,𝑧

Proof of Theorem nfeqf2OLD
StepHypRef Expression
1 exnal 1911 . 2 (∃𝑥 ¬ 𝑥 = 𝑦 ↔ ¬ ∀𝑥 𝑥 = 𝑦)
2 nfnf1 2197 . . 3 𝑥𝑥 𝑧 = 𝑦
3 ax13lem2 2462 . . . . 5 𝑥 = 𝑦 → (∃𝑥 𝑧 = 𝑦𝑧 = 𝑦))
4 ax13lem1 2421 . . . . 5 𝑥 = 𝑦 → (𝑧 = 𝑦 → ∀𝑥 𝑧 = 𝑦))
53, 4syld 47 . . . 4 𝑥 = 𝑦 → (∃𝑥 𝑧 = 𝑦 → ∀𝑥 𝑧 = 𝑦))
6 df-nf 1864 . . . 4 (Ⅎ𝑥 𝑧 = 𝑦 ↔ (∃𝑥 𝑧 = 𝑦 → ∀𝑥 𝑧 = 𝑦))
75, 6sylibr 225 . . 3 𝑥 = 𝑦 → Ⅎ𝑥 𝑧 = 𝑦)
82, 7exlimi 2252 . 2 (∃𝑥 ¬ 𝑥 = 𝑦 → Ⅎ𝑥 𝑧 = 𝑦)
91, 8sylbir 226 1 (¬ ∀𝑥 𝑥 = 𝑦 → Ⅎ𝑥 𝑧 = 𝑦)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wal 1635  wex 1859  wnf 1863
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1877  ax-4 1894  ax-5 2001  ax-6 2067  ax-7 2103  ax-10 2184  ax-12 2213  ax-13 2419
This theorem depends on definitions:  df-bi 198  df-an 385  df-or 866  df-ex 1860  df-nf 1864
This theorem is referenced by: (None)
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