Definition:Continuous Mapping (Metric Space)/Point/Definition 1

Definition
Let $M_1 = \struct {A_1, d_1}$ and $M_2 = \struct {A_2, d_2}$ be metric spaces.

Let $f: A_1 \to A_2$ be a mapping from $A_1$ to $A_2$.

Let $a \in A_1$ be a point in $A_1$.

$f$ is continuous at (the point) $a$ (with respect to the metrics $d_1$ and $d_2$) :
 * $\forall \epsilon \in \R_{>0}: \exists \delta \in \R_{>0}: \forall x \in A_1: \map {d_1} {x, a} < \delta \implies \map {d_2} {\map f x, \map f a} < \epsilon$

where $\R_{>0}$ denotes the set of all strictly positive real numbers.

Also known as
A mapping which is continuous at $a$ with respect to $d_1$ and $d_2$ can also be referred to as $\tuple {d_1, d_2}$-continuous at $a$.

Also see

 * Equivalence of Definitions of Metric Space Continuity at Point