 Some symbols that may be used to represent a contradiction include ↯, Opq, formula_19, ⊥, formula_20/ , and ※; in any symbolism, a contradiction may be substituted for the truth value "false", as symbolized, for instance, by "0" (as is common in boolean algebra).It is not uncommon to see Q.E.D., or some of its variants, immediately after a contradiction symbol.In fact, this often occurs in a proof by contradiction to indicate that the original assumption was false, and that its negation must therefore be true.