Definition:Sequential Continuity/Domain

Definition
Let $T_1 = \struct {S_1, \tau_1}$ and $T_2 = \struct {S_2, \tau_2}$ be topological spaces.

Let $f: S_1 \to S_2$ be a mapping.

$f$ is sequentially continuous on $T_1$ $f$ is sequentially continuous at $x$ for every $x \in T_1$.

At a Point
Let us recall: