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Metamath Proof Explorer

Theorem pm2.81

Description: Theorem *2.81 of WhiteheadRussell p. 108. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.81 ⊢ ψ → χ → θ → φ ∨ ψ → φ ∨ χ → φ ∨ θ

Proof

Step Hyp Ref Expression
1 orim2 ⊢ ψ → χ → θ → φ ∨ ψ → φ ∨ χ → θ
2 pm2.76 ⊢ φ ∨ χ → θ → φ ∨ χ → φ ∨ θ
3 1 2 syl6 ⊢ ψ → χ → θ → φ ∨ ψ → φ ∨ χ → φ ∨ θ