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Metamath Proof Explorer

Theorem pm2.53

Description: Theorem *2.53 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.53 ( ( 𝜑 ∨ 𝜓 ) → ( ¬ 𝜑 → 𝜓 ) )

Proof

Step Hyp Ref Expression
1 df-or ⊢ ( ( 𝜑 ∨ 𝜓 ) ↔ ( ¬ 𝜑 → 𝜓 ) )
2 1 biimpi ⊢ ( ( 𝜑 ∨ 𝜓 ) → ( ¬ 𝜑 → 𝜓 ) )