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Metamath Proof Explorer

Theorem pm1.2

Description: Axiom *1.2 of WhiteheadRussell p. 96, which they call "Taut". (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm1.2 ( ( 𝜑 ∨ 𝜑 ) → 𝜑 )

Proof

Step Hyp Ref Expression
1 id ⊢ ( 𝜑 → 𝜑 )
2 1 1 jaoi ⊢ ( ( 𝜑 ∨ 𝜑 ) → 𝜑 )