Theorem pm2.5g

Description: General instance of Theorem *2.5 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 9-Oct-2012)

	Ref	Expression
Assertion	pm2.5g	⊢ ( ¬ ( 𝜑 → 𝜓 ) → ( ¬ 𝜑 → 𝜒 ) )

Proof

Step	Hyp	Ref	Expression
1		simplim	⊢ ( ¬ ( 𝜑 → 𝜓 ) → 𝜑 )
2	1	pm2.24d	⊢ ( ¬ ( 𝜑 → 𝜓 ) → ( ¬ 𝜑 → 𝜒 ) )