I have a sequence $a_{i,n}$. Given that $\sup_{i}\lim_{n}|a_{i,n}|=0$, if I want $|a_{i,n}|<\epsilon$ for a particular $\epsilon>0$ for all $i$, for large enough $n$, can we find a $n$ such that it is independent of $i$?
One thing I tried is to prove this by contradiction. Assume the $n$ goes to infinity when $i$ goes to infinity, but then I don't know how to proceed.
No, of course not: take any sequence that satisfies the given property and then redefine it by setting $a_{n, n} = n$.