Image of Computable Real Number over Sequentially Computable Real Function is Computable

Theorem
Let $f : \R \to \R$ be a sequentially computable real function.

Let $a \in \R$ be a computable real number.

Then, $\map f a$ is a computable real number.

Proof
Let $\sequence {x_n}$ be defined as:
 * $x_n = a$

By Constant Sequence of Computable Real Number is Computable:
 * $\sequence {x_n}$ is a computable real sequence.

As $f$ is sequentially computable:
 * $\sequence {\map f {x_n}}$ is computable.

By Term of Computable Real Sequence is Computable:
 * $\map f {x_0}$ is computable.

But, $x_0 = a$ by definition.

Thus:
 * $\map f a$ is computable.