Exponent Combination Laws/Product of Powers/Proof 2/Lemma

Theorem
Let $a, b \in \R_{> 0}$

Let $a^{r}$ denote $a$ to the power of $r$. Let $I$ be some bounded  interval.

Let $\alpha, \beta$ be the endpoints of $I$.

Let $a^{r}$ and $b^{r}$ be restricted to $I \cap \Q$.

Let $m = \min \left\{ { a^{\alpha}, a^{\beta}, b^{\alpha}, b^{\beta} } \right\}$, $M = \max \left\{ { a^{\alpha}, a^{\beta}, b^{\alpha}, b^{\beta} } \right\}$.

Let $\epsilon \in \R_{>0}$.

Then:
 * $\left\vert{ a^{x} - a^{r} }\right\vert < \epsilon \land \left\vert{ b^{y} - b^{s} }\right\vert < \epsilon \implies \left\vert{ a^{x}b^{y} - a^{r}b^{s} }\right\vert < \epsilon \left({ 2M + 1 }\right)$

Proof
Let $m' = \min \left\{ { m, 1 } \right\}$.

Case 1: $\epsilon < m'$
Suppose $\epsilon < m'$.

Case 2: $\epsilon \geq m'$
Suppose $\epsilon \geq m'$.

Let $\delta \in \left({0 \,.\,.\, m'}\right)$.

Then:

Hence the result.