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Theorem ax12v2 2177
 Description: It is possible to remove any restriction on 𝜑 in ax12v 2176. Same as Axiom C8 of [Monk2] p. 105. Use ax12v 2176 instead when sufficient. (Contributed by NM, 5-Aug-1993.) Remove dependencies on ax-10 2142 and ax-13 2379. (Revised by Jim Kingdon, 15-Dec-2017.) (Proof shortened by Wolf Lammen, 8-Dec-2019.)
Assertion
Ref Expression
ax12v2 (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦𝜑)))
Distinct variable group:   𝑥,𝑦
Allowed substitution hints:   𝜑(𝑥,𝑦)

Proof of Theorem ax12v2
Dummy variable 𝑧 is distinct from all other variables.
StepHypRef Expression
1 equtrr 2029 . . 3 (𝑦 = 𝑧 → (𝑥 = 𝑦𝑥 = 𝑧))
2 ax12v 2176 . . . 4 (𝑥 = 𝑧 → (𝜑 → ∀𝑥(𝑥 = 𝑧𝜑)))
31imim1d 82 . . . . 5 (𝑦 = 𝑧 → ((𝑥 = 𝑧𝜑) → (𝑥 = 𝑦𝜑)))
43alimdv 1917 . . . 4 (𝑦 = 𝑧 → (∀𝑥(𝑥 = 𝑧𝜑) → ∀𝑥(𝑥 = 𝑦𝜑)))
52, 4syl9r 78 . . 3 (𝑦 = 𝑧 → (𝑥 = 𝑧 → (𝜑 → ∀𝑥(𝑥 = 𝑦𝜑))))
61, 5syld 47 . 2 (𝑦 = 𝑧 → (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦𝜑))))
7 ax6evr 2022 . 2 𝑧 𝑦 = 𝑧
86, 7exlimiiv 1932 1 (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦𝜑)))
 Colors of variables: wff setvar class Syntax hints:   → wi 4  ∀wal 1536 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-12 2175 This theorem depends on definitions:  df-bi 210  df-an 400  df-ex 1782 This theorem is referenced by:  sb56OLD  2275  equs5av  2276  wl-lem-exsb  34986  wl-lem-moexsb  34988
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