def normalize
      return unless book_id and ranges
      book_name + ' ' +
      ranges.map do |(ref_from, ref_to)|
        if ref_from != ref_to
          ref_part(ref_from) + '-' + ref_part(ref_to)
        else
          ref_part(ref_from)
        end
      end.join(',')
    end
def normalize
      return unless book_id and ranges
      book_name + ' ' +
      ranges.map do |(ref_from, ref_to)|
        if ref_from != ref_to
          ref_part(ref_from) + '-' + ref_part(ref_to)
        else
          ref_part(ref_from)
        end
      end.join(',')
    end
Returns a normalized passage reference. e.g.

 'JOHN 3:16&17' => 'John 3:16,17'