# File lib/rd/reference-resolver.rb, line 43
    def each_label
      tmp = []
      labels.each_value do |i|
        i.each do |j|
          tmp.push(j)
        end
      end
      tmp.sort{|i,j| i[1] <=> j[1]}.each do |i|
        yield(i[0])
      end
    end