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Metamath Proof Explorer

Theorem pm4.24

Description: Theorem *4.24 of WhiteheadRussell p. 117. (Contributed by NM, 11-May-1993)

Ref Expression
Assertion pm4.24 ( 𝜑 ↔ ( 𝜑 ∧ 𝜑 ) )

Proof

Step Hyp Ref Expression
1 id ⊢ ( 𝜑 → 𝜑 )
2 1 pm4.71i ⊢ ( 𝜑 ↔ ( 𝜑 ∧ 𝜑 ) )