Theorem pm2.52 646

Description: Theorem *2.52 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.) (Revised by Mario Carneiro, 31-Jan-2015.)

Assertion

Ref	Expression
pm2.52	⊢ (¬ (𝜑 → 𝜓) → (¬ 𝜑 → ¬ 𝜓))

Proof of Theorem pm2.52

Step	Hyp	Ref	Expression
1		conax1k 644	1 ⊢ (¬ (𝜑 → 𝜓) → (¬ 𝜑 → ¬ 𝜓))

Syntax hints:  ¬ wn 3   → wi 4

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-in1 604  ax-in2 605

This theorem is referenced by:  pm2.521dcALT  860