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)