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Metamath Proof Explorer

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 ) )