code: func (set StringSet) Union(other StringSet) StringSet {
  	unionedSet := NewStringSet()
  
  	for elem := range set {
  		unionedSet.Add(elem)
  	}
  	for elem := range other {
  		unionedSet.Add(elem)
  	}
  	return unionedSet
  }
docs: // Returns a new set with all items in both sets.