code: func (it *Int64) Next(ctx context.Context) bool {
  	graph.NextLogIn(it)
  	it.runstats.Next += 1
  	if it.at == -1 {
  		return graph.NextLogOut(it, false)
  	}
  	val := it.at
  	it.at = it.at + 1
  	if it.at > it.max {
  		it.at = -1
  	}
  	it.result = val
  	return graph.NextLogOut(it, true)
  }
docs: // Next() on an Int64 all iterator is a simple incrementing counter.
  // Return the next integer, and mark it as the result.