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 m,n being odd Element of NAT st m <= n & n <= len W & W.m = W.n
  holds W.cut(1,m).last() = W.cut(n,len W).first() by Lm28;
