# Combination Theorem for Continuous Mappings/Normed Division Ring/Multiple Rule

## Theorem

Let $\struct {S, \tau_{_S} }$ be a topological space.

Let $\struct {R, +, *, \norm {\,\cdot\,} }$ be a normed division ring.

Let $\tau_{_R}$ be the topology induced by the norm $\norm{\,\cdot\,}$.

Let $\lambda \in R$.

Let $f: \struct {S, \tau_{_S} } \to \struct {R, \tau_{_R} }$ be a continuous mappings.

Let $\lambda * f: S \to R$ be the mapping defined by:

$\forall x \in S: \map {\paren {\lambda * f} } x = \lambda * \map f x$

Let $f * \lambda: S \to R$ be the mapping defined by:

$\forall x \in S: \map {\paren {f * \lambda} } x = \map f x * \lambda$

Then:

$\lambda * f: \struct {S, \tau_{_S} } \to \struct {R, \tau_{_R} }$ is continuous
$f * \lambda: \struct {S, \tau_{_S} } \to \struct {R, \tau_{_R} }$ is continuous.

## Proof

$\struct {R, +, *, \tau_{_R} }$ is a topological division ring.
$\lambda * f, f * \lambda: \struct {S, \tau_{_S} } \to \struct {R, \tau_{_R} }$ are continuous mappings.

$\blacksquare$