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) Note that A is closed, therefore for every point limit $z$ of A we have that $z\in A$   ,also note that every point of A is limit point because $(a, b)\in A$ la sequence $(a_n) =\{(a, b+\frac{1}{n})\}$ is of points of A and $(a_n)\rightarrow (a, b)$.
2)  The set of the points limit of B is $B\,\,'=\{x^2 +y^2=1\}$.
