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 n being even Element of NAT st 1 <= n & n <= len W holds n div 2
  in dom W.edgeSeq() & W.n = W.edgeSeq().(n div 2) by Lm40;
