disjunction,
alternation, or logical sum, n. (Logic) 1. the binary truth-functional sentential connective that forms a compound sentence from two given sentences and corresponds to the English or. Inclusive disjunction assigns the value true whenever either or both of its arguments is true, and false only when both are false; exclusive disjunction assigns the value true if and only if one but not both of its disjuncts is true; it is thus sometimes called non-equivalence. The truth-tables for both functions are given by
2. a sentence so formed. The inclusive disjunction of P and Q is usually written P ∨ Q and sometimes read `P vel Q'; the less common exclusive disjunction has no standard symbol, but is sometimes written P ∨_ Q and read `P aut Q'. Since exclusive disjunction is equivalent to non-equivalence it is also sometimes written P ≠ Q.