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Metamath Proof Explorer

Theorem pm2.67-2

Description: Slight generalization of Theorem *2.67 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.67-2 ⊢ φ ∨ χ → ψ → φ → ψ

Proof

Step Hyp Ref Expression
1 orc ⊢ φ → φ ∨ χ
2 1 imim1i ⊢ φ ∨ χ → ψ → φ → ψ