reserve G for Graph,
  k, m, n for Nat;
reserve G for non void Graph;

theorem Th16:
  for oc being directed non empty Chain of G st oc is cyclic holds
  (vertex-seq oc).1 = (vertex-seq oc).(len oc +1)
proof
  let oc be directed non empty Chain of G;
  assume
A1: oc is cyclic;
  set vsoc = vertex-seq oc;
A2: vsoc is_vertex_seq_of oc by GRAPH_2:def 10;
  thus thesis by A1,A2,Th5;
end;
