Theorem pm2.51

Description: Theorem *2.51 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.51	⊢ ( ¬ ( 𝜑 → 𝜓 ) → ( 𝜑 → ¬ 𝜓 ) )

Proof

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