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Metamath Proof Explorer

Theorem pm5.5

Description: Theorem *5.5 of WhiteheadRussell p. 125. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm5.5 ( 𝜑 → ( ( 𝜑 → 𝜓 ) ↔ 𝜓 ) )

Proof

Step Hyp Ref Expression
1 biimt ⊢ ( 𝜑 → ( 𝜓 ↔ ( 𝜑 → 𝜓 ) ) )
2 1 bicomd ⊢ ( 𝜑 → ( ( 𝜑 → 𝜓 ) ↔ 𝜓 ) )