Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  z : V.t
  x : V.t
  y : V.t
  z0 : V.t
  e0 : EdgeOf G x y
  p : PathOf G y z0
  e : EdgeOf G z0 z
  IHp : forall e : EdgeOf G z0 z,
        weight (PathOf_add_end p e) = weight p + e.π1
  ============================
   (e0.π1 + (weight p + e.π1) = e0.π1 + weight p + e.π1)


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