# File lib/nanoc3/base/directed_graph.rb, line 146
    def edges
      result = []
      @vertices.each_with_index do |v, i|
        direct_successors_of(v).map { |v2| @vertice_indexes[v2] }.each do |i2|
          result << [ i, i2 ]
        end
      end
      result
    end