Theorem pm2.521g2

Description: A general instance of Theorem *2.521 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 8-Oct-2012)

	Ref	Expression
Assertion	pm2.521g2	⊢ ( ¬ ( 𝜑 → 𝜓 ) → ( 𝜒 → 𝜑 ) )

Proof

Step	Hyp	Ref	Expression
1		simplim	⊢ ( ¬ ( 𝜑 → 𝜓 ) → 𝜑 )
2	1	a1d	⊢ ( ¬ ( 𝜑 → 𝜓 ) → ( 𝜒 → 𝜑 ) )