Theorem pm2.25

Description: Theorem *2.25 of WhiteheadRussell p. 104. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.25	⊢ ( 𝜑 ∨ ( ( 𝜑 ∨ 𝜓 ) → 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		orel1	⊢ ( ¬ 𝜑 → ( ( 𝜑 ∨ 𝜓 ) → 𝜓 ) )
2	1	orri	⊢ ( 𝜑 ∨ ( ( 𝜑 ∨ 𝜓 ) → 𝜓 ) )