Theorem necon4d 3043

Description: Contrapositive inference for inequality. (Contributed by NM, 2-Apr-2007.) (Proof shortened by Andrew Salmon, 25-May-2011.)

Hypothesis

Ref	Expression
necon4d.1	⊢ (𝜑 → (𝐴 ≠ 𝐵 → 𝐶 ≠ 𝐷))

Assertion

Ref	Expression
necon4d	⊢ (𝜑 → (𝐶 = 𝐷 → 𝐴 = 𝐵))

Proof of Theorem necon4d

Step	Hyp	Ref	Expression
1		necon4d.1	. . 3 ⊢ (𝜑 → (𝐴 ≠ 𝐵 → 𝐶 ≠ 𝐷))
2	1	necon2bd 3035	. 2 ⊢ (𝜑 → (𝐶 = 𝐷 → ¬ 𝐴 ≠ 𝐵))
3		nne 3023	. 2 ⊢ (¬ 𝐴 ≠ 𝐵 ↔ 𝐴 = 𝐵)
4	2, 3	syl6ib 253	1 ⊢ (𝜑 → (𝐶 = 𝐷 → 𝐴 = 𝐵))

Syntax hints:  ¬ wn 3   → wi 4   = wceq 1536   ≠ wne 3019

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 209  df-ne 3020

This theorem is referenced by:  oa00  8188  map0g  8451  epfrs  9176  fin23lem24  9747  abs00  14652  oddvds  18678  isabvd  19594  01eq0ring  20048  uvcf1  20939  lindff1  20967  hausnei2  21964  dfconn2  22030  hausflimi  22591  hauspwpwf1  22598  cxpeq0  25264  his6  28879  fnpreimac  30419  lkreqN  36310  ltrnideq  37315  hdmapip0  39055  rpnnen3  39635