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
  for W1 being Walk of G, W2 being Subwalk of W1, W3 being Subwalk of W2
  holds W3 is Subwalk of W1 by Lm71;
