# File Warshall.rb, line 176
        def to_s
                        return "{}" if @basis == nil
                        str = "Basismenge: \n   " + @basis.to_s + "\n" +
                        "Adjazenzliste (Vorgaenger): \n   " + @vor.to_s + "\n"+
                        "Adjazenzliste (Nachfolger): \n   " + @nach.to_s + "\n \n"
                        return str
        end