func (u UserSet) union(o UserSet) UserSet {
return UserSet(sets.String(u).Union(sets.String(o)))
}
func (u UserSet) intersection(o UserSet) UserSet {
return UserSet(sets.String(u).Intersection(sets.String(o)))
}
// List makes a list from the set
func (u UserSet) List() []string {
return sets.String(u).List()
}