Theorem ax12v2 2173

Description: It is possible to remove any restriction on 𝜑 in ax12v 2172. Same as Axiom C8 of [Monk2] p. 105. Use ax12v 2172 instead when sufficient. (Contributed by NM, 5-Aug-1993.) Remove dependencies on ax-10 2137 and ax-13 2372. (Revised by Jim Kingdon, 15-Dec-2017.) (Proof shortened by Wolf Lammen, 8-Dec-2019.)

Assertion

Ref	Expression
ax12v2	⊢ (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑)))

Distinct variable group:   𝑥,𝑦

Allowed substitution hints:   𝜑(𝑥,𝑦)

Proof of Theorem ax12v2

Dummy variable 𝑧 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		equtrr 2025	. . 3 ⊢ (𝑦 = 𝑧 → (𝑥 = 𝑦 → 𝑥 = 𝑧))
2		ax12v 2172	. . . 4 ⊢ (𝑥 = 𝑧 → (𝜑 → ∀𝑥(𝑥 = 𝑧 → 𝜑)))
3	1	imim1d 82	. . . . 5 ⊢ (𝑦 = 𝑧 → ((𝑥 = 𝑧 → 𝜑) → (𝑥 = 𝑦 → 𝜑)))
4	3	alimdv 1919	. . . 4 ⊢ (𝑦 = 𝑧 → (∀𝑥(𝑥 = 𝑧 → 𝜑) → ∀𝑥(𝑥 = 𝑦 → 𝜑)))
5	2, 4	syl9r 78	. . 3 ⊢ (𝑦 = 𝑧 → (𝑥 = 𝑧 → (𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑))))
6	1, 5	syld 47	. 2 ⊢ (𝑦 = 𝑧 → (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑))))
7		ax6evr 2018	. 2 ⊢ ∃𝑧 𝑦 = 𝑧
8	6, 7	exlimiiv 1934	1 ⊢ (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑)))

Syntax hints:   → wi 4  ∀wal 1537

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1798  ax-4 1812  ax-5 1913  ax-6 1971  ax-7 2011  ax-12 2171

This theorem depends on definitions:  df-bi 206  df-an 397  df-ex 1783

This theorem is referenced by:  sbalex  2235  equs5av  2271  wl-lem-exsb  35721  wl-lem-moexsb  35723