3 Quantifers

• $\forall x: P(x)$ : for all $x$ , $P(x)$ is true
• $\exists x: P(x)$ : there exists $x$ such that $P(x)$ is true
• $\neg(\forall x: P(x)) \equiv \exists x: \neg P(x)$
• $\neg(\exists x: P(x)) \equiv \forall x: \neg P(x)$