# Subspace of Riemann Integrable Functions

## Theorem

Let $\mathbb J = \set {x \in \R: a \le x \le b}$ be a closed interval of the real number line $\R$.

Let $\map \RR {\mathbb J}$ be the set of all Riemann integrable functions on $\mathbb J$.

Then $\struct {\map \RR {\mathbb J}, +, \times}_\R$ is a subspace of the $\R$-vector space $\struct {\R^{\mathbb J}, +, \times}_\R$.

## Proof

Note that by definition, $\map {\mathcal D} {\mathbb J} \subseteq \R^{\mathbb J}$.

Let $f, g \in \map \RR {\mathbb J}$.

Let $\lambda \in \R$.

$f + \lambda g$ is Riemann integrable on $\mathbb J$.

That is:

$f + \lambda g \in \map \RR {\mathbb J}$
$\struct {\map \RR {\mathbb J}, +, \times}_\R$ is a subspace of $\struct {\R^{\mathbb J}, +, \times}_\R$.

$\blacksquare$