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The source of the following topic is $\text{Section 5 (Measure and integration), Chapter II}$ of the book $\text{$p$-adic numbers, $p$-adic analysis and zeta functions}$.
by $\text{Neal koblitz}$ :
The $p$-adic field $\mathbb{Q}_p$ has topological basis of open sets of the form $a+p^N \mathbb{Z}_...
