code: func NewFixed(vals ...graph.Value) *Fixed {
  	it := &Fixed{
  		uid:    NextUID(),
  		values: make([]graph.Value, 0, 20),
  	}
  	for _, v := range vals {
  		it.Add(v)
  	}
  	return it
  }
docs: // Creates a new Fixed iterator with a custom comparator.