# File Warshall.rb, line 238
        def vereinigt(rel)
                erg=Relation.new([[]])
                erg.basis!(@basis + rel.basis)
                        erg.each{|i| if @nach[i]!=nil then erg.nach[i] = @nach[i] + rel.nach[i] else erg.nach[i] = Menge.new([]) + rel.nach[i]end}
                        erg.each{|i| if @vor[i]!=nil then erg.vor[i] = @vor[i] + rel.vor[i] else erg.vor[i] = Menge.new([]) + rel.vor[i]end}
                        return erg
        end