Theorem ax8dfeq 30948

Description: A version of ax-8 1979 for use with defined equality. (Contributed by Scott Fenton, 12-Dec-2010.)

Assertion

Ref	Expression
ax8dfeq	⊢ ∃𝑧((𝑧 ∈ 𝑥 → 𝑧 ∈ 𝑦) → (𝑤 ∈ 𝑥 → 𝑤 ∈ 𝑦))

Proof of Theorem ax8dfeq

Step	Hyp	Ref	Expression
1		ax6e 2238	. 2 ⊢ ∃𝑧 𝑧 = 𝑤
2		ax8 1983	. . . 4 ⊢ (𝑤 = 𝑧 → (𝑤 ∈ 𝑥 → 𝑧 ∈ 𝑥))
3	2	equcoms 1934	. . 3 ⊢ (𝑧 = 𝑤 → (𝑤 ∈ 𝑥 → 𝑧 ∈ 𝑥))
4		ax8 1983	. . 3 ⊢ (𝑧 = 𝑤 → (𝑧 ∈ 𝑦 → 𝑤 ∈ 𝑦))
5	3, 4	imim12d 79	. 2 ⊢ (𝑧 = 𝑤 → ((𝑧 ∈ 𝑥 → 𝑧 ∈ 𝑦) → (𝑤 ∈ 𝑥 → 𝑤 ∈ 𝑦)))
6	1, 5	eximii 1754	1 ⊢ ∃𝑧((𝑧 ∈ 𝑥 → 𝑧 ∈ 𝑦) → (𝑤 ∈ 𝑥 → 𝑤 ∈ 𝑦))

Syntax hints:   → wi 4  ∃wex 1695

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1713  ax-4 1728  ax-5 1827  ax-6 1875  ax-7 1922  ax-8 1979  ax-12 2034  ax-13 2234

This theorem depends on definitions:  df-bi 196  df-an 385  df-ex 1696

This theorem is referenced by: (None)