In logics and mathematics, negation (from Latin negare `to deny') is the unary operation ``$\lnot$ '' which swaps the truth value of any operand to the opposite truth value. So, if the statement $P$ is true then its negated statement $\lnot P$ is false, and vice versa.

Note 1. The negated statement $\lnot P$ (by Heyting) has been denoted also with $-P$ (Peano), $\sim\! P$ (Russell), $\overline{P}$ (Hilbert) and $NP$ (by the Polish notation).

Note 2. $\lnot P$ may be expressed by implication as $$P\to\curlywedge$$ where $\curlywedge$ means any contradictory statement.

Note 3. The negation of logical or and logical and give the results $$\lnot(P\lor Q) \equiv \lnot P \land \lnot Q,\;\;\; \lnot(P\land Q) \equiv \lnot P \lor \lnot Q.$$ Analogical results concern the quantifier statements: $$\lnot (\exists x)P(x) \equiv (\forall x)\lnot P(x),\;\;\; \lnot (\forall x)P(x) \equiv (\exists x)\lnot P(x).$$ These all are known as de Morgan's laws.

Note 4. Many mathematical relation statements, expressed with such special relation symbols as $=,\, \subseteq,\, \in,\, \cong,\, \parallel,\, \mid$ , are negated by using in the symbol an additional cross line: $\neq,\, \nsubseteq,\, \notin,\, \ncong,\, \nparallel,\, \nmid$ .