Metamath Proof Explorer

Theorem pm2.75

Description: Theorem *2.75 of WhiteheadRussell p. 108. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 4-Jan-2013)

Ref Expression
Assertion pm2.75 ⊢ φ ∨ ψ → φ ∨ ψ → χ → φ ∨ χ

Proof

Step Hyp Ref Expression
1 pm2.76 ⊢ φ ∨ ψ → χ → φ ∨ ψ → φ ∨ χ
2 1 com12 ⊢ φ ∨ ψ → φ ∨ ψ → χ → φ ∨ χ