Theorem pm2.54

Description: Theorem *2.54 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.54	⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( 𝜑 ∨ 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		df-or	⊢ ( ( 𝜑 ∨ 𝜓 ) ↔ ( ¬ 𝜑 → 𝜓 ) )
2	1	biimpri	⊢ ( ( ¬ 𝜑 → 𝜓 ) → ( 𝜑 ∨ 𝜓 ) )