Strictly Positive Real Numbers are Closed under Division

Theorem
The set $\R_+^*$ of strictly positive real numbers is closed under division:
 * $\forall a, b \in \R_+^*: a \div b \in \R_+^*$

Proof
From the definition of division:
 * $a \div b := a \times \left({\dfrac 1 b}\right)$

where $\dfrac 1 b$ is the inverse for real number multiplication.

As the algebraic structure $\left({\R_+^*, \times}\right)$ forms a group, it follows that:
 * $\forall a, b \in \R: a \times \left({\dfrac 1 b}\right) \in \R$

Therefore real number division is closed.