# File Warshall.rb, line 108
        def initialize(rel)
                @vor = Hash.new()
                @nach = Hash.new()
                @basis=Menge.new([]) 
                if rel!=[[]]
                @basis=Menge.new([])
                rel.each{|i| @basis.add(i[0]);@basis.add(i[1])}
          each {|i| @vor[i]=berechneVorgaenger(i,rel)}
          each {|i| @nach[i]=berechneNachfolger(i,rel)}
                end
        end