Mergelyan-Wesler Theorem

Theorem
Let $P = \sequence {D_1, D_2, \dotsc}$ be an infinite sequence of disjoint open disks whose union is almost everywhere the unit disk $D$.

Let $r_n$ be the radius of $D_n$.

Then:
 * $\displaystyle \sum_{k \mathop = 1}^\infty r_k = +\infty$