Theorem pm2.521 177

Description: Theorem *2.521 of [WhiteheadRussell] p. 107. Instance of pm2.521g 175 and of pm2.521g2 176. (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 175	1 ⊢ (¬ (𝜑 → 𝜓) → (𝜓 → 𝜑))

This proof depends on syntax axioms:  ¬ wn 3   → wi 4

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem is used by:  impimprbi  841  ifpimim  44263