reserve G,G1,G2 for _Graph;
reserve W,W1,W2 for Walk of G;
reserve e,x,y,z for set;
reserve v for Vertex of G;
reserve n,m for Element of NAT;

theorem Th86:
  W.first() in W.vertices() & W.last() in W.vertices()
proof
  1 <= len W by ABIAN:12;
  hence W.first() in W.vertices() by Lm45,JORDAN12:2;
  thus thesis by Lm45;
end;
