Set Complement/Examples/Positive Real Numbers in Complex Numbers

Example of Set Complement
Let the universe $\Bbb U$ be defined to be the set of real numbers $\C$.

Let the set of (strictly) positive real numbers be denoted by $\R_{>0}$.

Then:
 * $\relcomp {} {\R_{>0} } = \set {x + i y: y \ne 0 \text { or } x \le 0}$