Theorem pm5.12

Description: Theorem *5.12 of WhiteheadRussell p. 123. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm5.12	⊢ ( ( 𝜑 → 𝜓 ) ∨ ( 𝜑 → ¬ 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		pm2.51	⊢ ( ¬ ( 𝜑 → 𝜓 ) → ( 𝜑 → ¬ 𝜓 ) )
2	1	orri	⊢ ( ( 𝜑 → 𝜓 ) ∨ ( 𝜑 → ¬ 𝜓 ) )