What is the basis of $ \Bbb{Q}_p$ as topological space?
My try: The local basis at $a$ is given by {$x∈\Bbb{Q}_p｜｜x-a｜_p＜p^{-n}$, $n∈\Bbb{Z}$・・・①}
① is equivalent to $ord_p(x-a)＞n$・・・②. But I cannot proceed from here, I thought at first that ② is equivalent to $x-a∈p^n \Bbb{Q}$. But this is meaningless because $p^n \Bbb{Q}＝\Bbb{Q}$. So I should have made some mistake. I believe the basis is written like {$a +p^n◾️$}, but I'm having trouble how to find ◾️.