Sequence of Powers of Number less than One/Necessary Condition/Proof 2

Proof
Let $\epsilon \in \R_{>0}$ be a strictly positive real number.

Suppose that:
 * $\exists N \in \N: \size x^N < \epsilon$

Then the result follows by the definition of a limit, because:
 * $\forall n \in \N: n \ge N \implies \size {x^n} = \size x^n \le \size x^N < \epsilon$

where Absolute Value Function is Completely Multiplicative is applied.

It remains to consider the case that:
 * $\forall n \in \N: \size x^n \ge \epsilon$

By the Archimedean Principle, we can choose a natural number $M$ such that:
 * $M > \dfrac 1 {\paren {1 - \size x} \epsilon}$

Then, by Sum of Geometric Sequence:
 * $\ds M \epsilon \le \sum_{k \mathop = 0}^{M - 1} \size x^k = \frac {1 - \size x^M} {1 - \size x} < M \epsilon$

a contradiction.

Hence the result.