def match_scalar(label)
      label = label.to_sym
      Factor.detect do |factor|
        return factor if factor.label == label or factor.abbreviation == label
      end
    end
def match_scalar(label)
      label = label.to_sym
      Factor.detect do |factor|
        return factor if factor.label == label or factor.abbreviation == label
      end
    end
Returns the Factor which matches the label, or nil if no match.