Theorem pm2.47

Description: Theorem *2.47 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.47	⊢ ( ¬ ( 𝜑 ∨ 𝜓 ) → ( ¬ 𝜑 ∨ 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		pm2.45	⊢ ( ¬ ( 𝜑 ∨ 𝜓 ) → ¬ 𝜑 )
2	1	orcd	⊢ ( ¬ ( 𝜑 ∨ 𝜓 ) → ( ¬ 𝜑 ∨ 𝜓 ) )