Limit points of sets Find all limit points of given sets:
$A = \left\{ (x,y)\in\mathbb{R}^2  : x\in \mathbb{Z}\right\}$
$B = \left\{ (x,y)\in\mathbb{R}^2  : x^2+y^2 >1 \right\}$
I don't know how to do that. Are there any standard ways to do this?

1) Is set A closed or not? If it is we're then done, otherwise there's some point not in it that is a limit point of A
2) As before but perhaps even easier.
