code: func (s *SyncedSet) Union(other *SyncedSet) *SyncedSet {
  	newSet := NewSyncedSet()
  	for elt := range s.set {
  		newSet.Add(elt)
  	}
  	for elt := range other.set {
  		newSet.Add(elt)
  	}
  	return &newSet
  }
docs: // Union returns a pointer to a new set containing the union of current set and other