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Metamath Proof Explorer

Theorem pm1.4

Description: Axiom *1.4 of WhiteheadRussell p. 96. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm1.4 ⊢ φ ∨ ψ → ψ ∨ φ

Proof

Step Hyp Ref Expression
1 olc ⊢ φ → ψ ∨ φ
2 orc ⊢ ψ → ψ ∨ φ
3 1 2 jaoi ⊢ φ ∨ ψ → ψ ∨ φ