code: func (it *And) SubIterators() []graph.Iterator {
  	iters := make([]graph.Iterator, 0, len(it.internalIterators)+1)
  	if it.primaryIt != nil {
  		iters = append(iters, it.primaryIt)
  	}
  	iters = append(iters, it.internalIterators...)
  	return iters
  }
docs: // Returns a slice of the subiterators, in order (primary iterator first).