Power Function on Base between Zero and One is Strictly Decreasing/Rational Number

Theorem
Let $a \in \R$.

Let $0 < a < 1$.

Let $f : \Q \to \R$ be the real mapping defined as:
 * $f \left({ q }\right) = a^q$

where $a^q$ denotes $a$ to the power of $q$.

Then $f$ is strictly decreasing.

Proof
Let $\dfrac{r}{s}, \dfrac{t}{u} \in \Q$, where $r, t \in \Z, s, u \in \Z_{>0}$.