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 ¬φφψψ

Proof

Step Hyp Ref Expression
1 pm2.53 φψ¬φψ
2 1 com12 ¬φφψψ