Metamath Proof Explorer

Theorem pm2.21

Description: From a wff and its negation, anything follows. Theorem *2.21 of WhiteheadRussell p. 104. Also called the Duns Scotus law. Its commuted form is pm2.24 and its associated inference is pm2.21i . (Contributed by NM, 29-Dec-1992) (Proof shortened by Wolf Lammen, 14-Sep-2012)

Ref Expression
Assertion pm2.21 ¬ φ φ ψ


Step Hyp Ref Expression
1 id ¬ φ ¬ φ
2 1 pm2.21d ¬ φ φ ψ