Function: setunion
Section: linear_algebra
C-Name: setunion
Prototype: GG
Help: setunion(x,y): union of the sets x and y.
Description:
 (vec, vec):vec        setunion($1, $2)
Doc: union of the two sets $x$ and $y$ (see \kbd{setisset}).
 If $x$ or $y$ is not a set, the result is undefined.
