@doskel \{x \in (\frac{-r}{\sqrt{2}},\frac{+r}{\sqrt{2}}):r\sqrt{2}-\sqrt{r^2-x^2},|x|\}
\{x \in (\frac{-r}{\sqrt{2}},\frac{+r}{\sqrt{2}}):r\sqrt{2}-\sqrt{r^2-x^2},|x|\}