Local Basis of P-adic Number/Cosets

Theorem
Let $p$ be a prime number.

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

Let $a \in \Q_p$. Let $\Z_p$ be the $p$-adic integers.

Then the set $\set {a + p^n \Z_p: n \in Z}$ is a local basis of $a$ consisting of clopen sets.

Proof
From Leigh.Samphier/Sandbox/Local Basis of P-adic Number the set $\set { \map {B_{p^{-n}}} a : n \in \Z}$ is a local basis of clopen sets.

From Open Balls of P-adic Number:
 * $\set { \map {B_{p^{-n}}} a : n \in \Z} = \set {a + p^{n+1} \Z_p : n \in \Z} = \set {a + p^n \Z_p : n \in \Z}$

The result follows.