Goal:
  
  G1 : t
  G2 : t
  sub : subgraph G1 G2
  acG2 : acyclic_no_loop G2
  x : V.t
  p : PathOf G1 x x
  _x_ : V.t
  _y_ : V.t
  _x1_ : Z
  _p_ : EdgeSet.In (_x_, _x1_, _y_) (E G1)
  ============================
   (_x1_ >= _x1_)


DEBUG:Going to execute:
intros; Zify.zify_pre_hook; zify_elim_let; zify_op;
            Zify.zify_iter_specs; Zify.zify_to_euclidean_division_equations;
            Zify.zify_post_hook