Theorem pm4.64

Description: Theorem *4.64 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm4.64	⊢ ( ( ¬ 𝜑 → 𝜓 ) ↔ ( 𝜑 ∨ 𝜓 ) )

Proof

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