Theorem eqeq12dOLD 2756

Description: Obsolete version of eqeq12d 2752 as of 23-Oct-2024. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 25-May-2011.) (New usage is discouraged.) (Proof modification is discouraged.)

Hypotheses

Ref	Expression
eqeq12dOLD.1	⊢ (𝜑 → 𝐴 = 𝐵)
eqeq12dOLD.2	⊢ (𝜑 → 𝐶 = 𝐷)

Assertion

Ref	Expression
eqeq12dOLD	⊢ (𝜑 → (𝐴 = 𝐶 ↔ 𝐵 = 𝐷))

Proof of Theorem eqeq12dOLD

Step	Hyp	Ref	Expression
1		eqeq12dOLD.1	. 2 ⊢ (𝜑 → 𝐴 = 𝐵)
2		eqeq12dOLD.2	. 2 ⊢ (𝜑 → 𝐶 = 𝐷)
3		eqeq12OLD 2755	. 2 ⊢ ((𝐴 = 𝐵 ∧ 𝐶 = 𝐷) → (𝐴 = 𝐶 ↔ 𝐵 = 𝐷))
4	1, 2, 3	syl2anc 584	1 ⊢ (𝜑 → (𝐴 = 𝐶 ↔ 𝐵 = 𝐷))

Syntax hints:   → wi 4   ↔ wb 206   = wceq 1539

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1794  ax-4 1808  ax-5 1909  ax-6 1966  ax-7 2006  ax-9 2117  ax-ext 2707

This theorem depends on definitions:  df-bi 207  df-an 396  df-ex 1779  df-cleq 2728

This theorem is referenced by:  eqeqan12dOLD  2757