Theorem pm2.6

Description: Theorem *2.6 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.6	⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( ( 𝜑 → 𝜓 ) → 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		id	⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( ¬ 𝜑 → 𝜓 ) )
2		idd	⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( 𝜓 → 𝜓 ) )
3	1 2	jad	⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( ( 𝜑 → 𝜓 ) → 𝜓 ) )