code: func (it *Int64) Stats() graph.IteratorStats {
  	s, exact := it.Size()
  	return graph.IteratorStats{
  		ContainsCost: 1,
  		NextCost:     1,
  		Size:         s,
  		ExactSize:    exact,
  		Next:         it.runstats.Next,
  		Contains:     it.runstats.Contains,
  	}
  }
docs: // Stats for an Int64 are simple. Super cheap to do any operation,
  // and as big as the range.