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
  e in W.edges() iff ex n being even Element of NAT st 1 <= n & n <= len
  W & W.n = e by Lm46;
