Continuous Mapping is Sequentially Continuous/Corollary

Theorem
Let $X$ and $Y$ be topological spaces.

Let $f: X \to Y$ be a mapping that is continuous at $x$.

Let $f$ be continuous (everywhere) on $X$.

Then $f$ is sequentially continuous on $X$.

Proof
This follows immediately from the definitions:
 * $(1): \quad$ A mapping is sequentially continuous everywhere in $X$ iff if it is sequentially continuous at each point
 * $(2): \quad$ A mapping is continuous everywhere on $X$ iff it is continuous at each point.