Find the numbers at which $f$ is discontinuous.

$$f(x) = \begin{cases} 1+x^2 & \textrm{if }x \leq 0 \\ 2-x & \textrm{if }0< x \leq 2 \\ (x-2)^2 & \textrm{if }x > 2 \end{cases}$$

If there are multiple discontinuities, separate the values with commas.