Image of Computable Real Number over Sequentially Computable Real Function is Computable
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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.
$\blacksquare$