Metamath Proof Explorer

Theorem orel1

Description: Elimination of disjunction by denial of a disjunct. Theorem *2.55 of WhiteheadRussell p. 107. (Contributed by NM, 12-Aug-1994) (Proof shortened by Wolf Lammen, 21-Jul-2012)

Ref Expression
Assertion orel1 ¬ φ φ ψ ψ


Step Hyp Ref Expression
1 pm2.53 φ ψ ¬ φ ψ
2 1 com12 ¬ φ φ ψ ψ