Theorem ax12v2 2180

Description: It is possible to remove any restriction on 𝜑 in ax12v 2179. Same as Axiom C8 of [Monk2] p. 105. Use ax12v 2179 instead when sufficient. (Contributed by NM, 5-Aug-1993.) Remove dependencies on ax-10 2142 and ax-13 2377. (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 2022	. . 3 ⊢ (𝑦 = 𝑧 → (𝑥 = 𝑦 → 𝑥 = 𝑧))
2		ax12v 2179	. . . 4 ⊢ (𝑥 = 𝑧 → (𝜑 → ∀𝑥(𝑥 = 𝑧 → 𝜑)))
3	1	imim1d 82	. . . . 5 ⊢ (𝑦 = 𝑧 → ((𝑥 = 𝑧 → 𝜑) → (𝑥 = 𝑦 → 𝜑)))
4	3	alimdv 1916	. . . 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 2015	. 2 ⊢ ∃𝑧 𝑦 = 𝑧
8	6, 7	exlimiiv 1931	1 ⊢ (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑)))

Syntax hints:   → wi 4  ∀wal 1538

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1795  ax-4 1809  ax-5 1910  ax-6 1967  ax-7 2008  ax-12 2178

This theorem depends on definitions:  df-bi 207  df-an 396  df-ex 1780

This theorem is referenced by:  ax12ev2  2181  sbalexOLD  2244  equs5av  2278  in-ax8  36247  ss-ax8  36248  wl-lem-exsb  37589  wl-lem-moexsb  37591