# File Warshall.rb, line 205
        def to_s
                        return "{}" if @basis == nil
                        str = "Basismenge: \n   " + @basis.to_s + "\n" +
                        "Adjazenzliste (Vorgaenger): \n   "
                        @vor.each_key{|i| str+= "\t"+i.to_s+" " + (@vor[i].to_s) + "\n"}
                        str+= "\n"
                        str+="Adjazenzliste (Nachfolger):\n   "
      @nach.each_key{|i| str+= "\t"+i.to_s+" " + (@nach[i].to_s) + "\n"}
                        return str
        end