Theorem pm2.521 178

Description: Theorem *2.521 of [WhiteheadRussell] p. 107. Instance of pm2.521g 176 and of pm2.521g2 177. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.521	⊢ (¬ (𝜑 → 𝜓) → (𝜓 → 𝜑))

Proof of Theorem pm2.521

Step	Hyp	Ref	Expression
1		pm2.521g 176	1 ⊢ (¬ (𝜑 → 𝜓) → (𝜓 → 𝜑))

Syntax hints:  ¬ wn 3   → wi 4

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

This theorem is referenced by:  impimprbi  826  ifpimim  39881