Definition:Continuous Real Function/Point

Definition
Let $A \subseteq \R$ be any subset of the real numbers, and $f: A \to \R$ be a real function.

Let $x \in A$ be a point of $A$.

Then $f$ is continuous at $x$ when the limit of $f \left({y}\right)$ as $y \to x$ exists and:
 * $\displaystyle \lim_{y \to x} \ f \left({y}\right) = f \left({x}\right)$

That is:
 * $\forall \epsilon \in \R_{>0}: \exists \delta \in \R_{>0}: \left\vert{y - x}\right\vert < \delta \implies \left\vert{f \left({y}\right) - f \left({x}\right)}\right\vert < \epsilon$