Theorem pm2.67

Description: Theorem *2.67 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.67	⊢ ( ( ( 𝜑 ∨ 𝜓 ) → 𝜓 ) → ( 𝜑 → 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		pm2.67-2	⊢ ( ( ( 𝜑 ∨ 𝜓 ) → 𝜓 ) → ( 𝜑 → 𝜓 ) )