Theorem necon4ddc 2277

Description: Contrapositive inference for inequality. (Contributed by Jim Kingdon, 17-May-2018.)

Hypothesis

Ref	Expression
necon4ddc.1	⊢ (𝜑 → (DECID 𝐴 = 𝐵 → (𝐴 ≠ 𝐵 → 𝐶 ≠ 𝐷)))

Assertion

Ref	Expression
necon4ddc	⊢ (𝜑 → (DECID 𝐴 = 𝐵 → (𝐶 = 𝐷 → 𝐴 = 𝐵)))

Proof of Theorem necon4ddc

Step	Hyp	Ref	Expression
1		necon4ddc.1	. . 3 ⊢ (𝜑 → (DECID 𝐴 = 𝐵 → (𝐴 ≠ 𝐵 → 𝐶 ≠ 𝐷)))
2		df-ne 2206	. . . 4 ⊢ (𝐴 ≠ 𝐵 ↔ ¬ 𝐴 = 𝐵)
3		df-ne 2206	. . . 4 ⊢ (𝐶 ≠ 𝐷 ↔ ¬ 𝐶 = 𝐷)
4	2, 3	imbi12i 228	. . 3 ⊢ ((𝐴 ≠ 𝐵 → 𝐶 ≠ 𝐷) ↔ (¬ 𝐴 = 𝐵 → ¬ 𝐶 = 𝐷))
5	1, 4	syl6ib 150	. 2 ⊢ (𝜑 → (DECID 𝐴 = 𝐵 → (¬ 𝐴 = 𝐵 → ¬ 𝐶 = 𝐷)))
6		condc 749	. 2 ⊢ (DECID 𝐴 = 𝐵 → ((¬ 𝐴 = 𝐵 → ¬ 𝐶 = 𝐷) → (𝐶 = 𝐷 → 𝐴 = 𝐵)))
7	5, 6	sylcom 25	1 ⊢ (𝜑 → (DECID 𝐴 = 𝐵 → (𝐶 = 𝐷 → 𝐴 = 𝐵)))

Syntax hints:  ¬ wn 3   → wi 4  DECID wdc 742   = wceq 1243   ≠ wne 2204

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in2 545  ax-io 630

This theorem depends on definitions:  df-bi 110  df-dc 743  df-ne 2206

This theorem is referenced by: (None)