
theorem
  not ex p being Path of KoenigsbergBridges st p is cyclic Eulerian
  proof
    reconsider v=0 as Vertex of KoenigsbergBridges by ENUMSET1:def 2;
    Degree v = 3 by d0; then
    Degree v is not even by POLYFORM:6;
    hence thesis by GRAPH_3:59;
  end;
