Theorem pm2.49

Description: Theorem *2.49 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.49	⊢ ( ¬ ( 𝜑 ∨ 𝜓 ) → ( ¬ 𝜑 ∨ ¬ 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		pm2.46	⊢ ( ¬ ( 𝜑 ∨ 𝜓 ) → ¬ 𝜓 )
2	1	olcd	⊢ ( ¬ ( 𝜑 ∨ 𝜓 ) → ( ¬ 𝜑 ∨ ¬ 𝜓 ) )