code: func (it *Regex) Optimize() (graph.Iterator, bool) {
  	newSub, changed := it.subIt.Optimize()
  	if changed {
  		it.subIt.Close()
  		it.subIt = newSub
  	}
  	return it, false
  }
docs: // There's nothing to optimize, locally, for a Regex iterator.
  // Replace the underlying iterator if need be.