Characterization of Closed Ball in P-adic Numbers

Theorem
Let $p$ be a prime number.

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

Let $\Z_p$ be the $p$-adic integers.

For any $\epsilon \in \R_{>0}$ and $a \in \Q_p$ let $\map {{B_\epsilon}^-} a$ denote the closed ball with center $a$ and radius $\epsilon$.

Let $x, y \in \Q_p$.

Let $n \in Z$.


 * $(1)\quad x \in \map {B^{\,-}_{p^{-n}}} y$
 * $(1)\quad x \in \map {B^{\,-}_{p^{-n}}} y$


 * $(2)\quad \norm{x -y}_p \le p^{-n}$


 * $(3)\quad x - y \in p^n \Z_p$