Theorem pm4.25

Description: Theorem *4.25 of WhiteheadRussell p. 117. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm4.25	⊢ ( 𝜑 ↔ ( 𝜑 ∨ 𝜑 ) )

Proof

Step	Hyp	Ref	Expression
1		oridm	⊢ ( ( 𝜑 ∨ 𝜑 ) ↔ 𝜑 )
2	1	bicomi	⊢ ( 𝜑 ↔ ( 𝜑 ∨ 𝜑 ) )