code: func moveTagsTo(dst graph.Iterator, src *And) {
  	tags := src.getSubTags()
  	for _, tag := range dst.Tagger().Tags() {
  		if _, ok := tags[tag]; ok {
  			delete(tags, tag)
  		}
  	}
  	dt := dst.Tagger()
  	for k := range tags {
  		dt.Add(k)
  	}
  }
docs: // moveTagsTo() gets the tags for all of the src's subiterators and the
  // src itself, and moves them to dst.