Sequence of P-adic Integers has Convergent Subsequence/Lemma 5

Theorem
Let $\struct {\Q_p, \norm {\,\cdot\,}_p}$ be the $p$-adic numbers for some prime $p$.

Let $\sequence{x_n}$ be a sequence of $p$-adic integers.

Let $\sequence{b_n}$ be a sequence of $p$-adic digits such that:
 * the canonical expansion $\ldots \, b_n \, \ldots \, b_1 b_0$ converges to $x \in \Q_p$

Let $\sequence{x_{n_rj}}_{j \mathop \in \N}$ be a subsequence of $\sequence{x_n}$:
 * for all $j \in \N$, the canonical expansion of $x_{n_j}$ begins with the $p$-adic digits $b_j \, \ldots \, b_1 b_0$

Then:
 * the subsequence $\sequence{x_{n_j}}_{j \mathop \in \N}$ converges to $x \in \Z_p$

Proof
By definition of the canonical expansion $\ldots \, b_n \, \ldots \, b_1 b_0$ converges to $x$:
 * the sequence of partial sums $\ds \sum_{n \mathop = 0}^j b_n p^n$ converges to $x$

Let $\sequence{y_j}$ be the sequence of partial sums:
 * $y_j = \ds \sum_{n \mathop = m}^j b_n p^n$

From Leigh.Samphier/Sandbox/Null Sequence Test for Convergence, it is sufficient to show that:
 * $\sequence{x_{n_j} - y_j}$ is a null sequence

For all $j \in \N$, we have:

From P-adic Norm of P-adic Expansion is determined by First Nonzero Coefficient:
 * $\norm{x_{n_j} - y_j}_p \le \dfrac 1 {p^{j+1}} < \dfrac 1 {p^j}$

From Sequence of Powers of Number less than One
 * $\ds \lim_{j \mathop \to \infty} \dfrac 1 {p^j} = 0$

From Squeeze Theorem for Real Sequences:
 * $\ds \lim_{j \mathop \to \infty} \norm{x_{n_j} - y_j}_p = 0$

By definition of convergence:
 * $\sequence{x_{n_j} - y_j}$ converges to $0$

It follows that $\sequence{x_{n_j} - y_j}$ is a null sequence by definition.