Theorem necon1idc 2258

Description: Contrapositive inference for inequality. (Contributed by Jim Kingdon, 16-May-2018.)

Hypothesis

Ref	Expression
necon1idc.1	⊢ (𝐴 ≠ 𝐵 → 𝐶 = 𝐷)

Assertion

Ref	Expression
necon1idc	⊢ (DECID 𝐴 = 𝐵 → (𝐶 ≠ 𝐷 → 𝐴 = 𝐵))

Proof of Theorem necon1idc

Step	Hyp	Ref	Expression
1		df-ne 2206	. . . 4 ⊢ (𝐴 ≠ 𝐵 ↔ ¬ 𝐴 = 𝐵)
2		necon1idc.1	. . . 4 ⊢ (𝐴 ≠ 𝐵 → 𝐶 = 𝐷)
3	1, 2	sylbir 125	. . 3 ⊢ (¬ 𝐴 = 𝐵 → 𝐶 = 𝐷)
4	3	a1i 9	. 2 ⊢ (DECID 𝐴 = 𝐵 → (¬ 𝐴 = 𝐵 → 𝐶 = 𝐷))
5	4	necon1aidc 2256	1 ⊢ (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-in1 544  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)