# File Warshall.rb, line 248
        def komp(rel)
                erg=Relation.new([[]])
                erg.basis!(@basis+rel.basis)
                        erg.each{|i| erg.nach[i]=Menge.new([]); erg.vor[i]=Menge.new([])}
                        erg.each{|i| @nach[i].each{|j| erg.nach[i]+=rel.nachfolger(j)}}
                        erg.each{|i| rel.vor[i].each{|j| erg.vor[i]+=vorgaenger(j)}}
                        return erg
        end