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Metamath Proof Explorer

Theorem pm2.45

Description: Theorem *2.45 of WhiteheadRussell p. 106. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.45 ( ¬ ( 𝜑 ∨ 𝜓 ) → ¬ 𝜑 )

Proof

Step Hyp Ref Expression
1 orc ⊢ ( 𝜑 → ( 𝜑 ∨ 𝜓 ) )
2 1 con3i ⊢ ( ¬ ( 𝜑 ∨ 𝜓 ) → ¬ 𝜑 )