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Metamath Proof Explorer

Theorem pm3.11

Description: Theorem *3.11 of WhiteheadRussell p. 111. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm3.11 ⊢ ¬ ¬ φ ∨ ¬ ψ → φ ∧ ψ

Proof

Step Hyp Ref Expression
1 anor ⊢ φ ∧ ψ ↔ ¬ ¬ φ ∨ ¬ ψ
2 1 biimpri ⊢ ¬ ¬ φ ∨ ¬ ψ → φ ∧ ψ