Goal:
  
  G : t
  l : labelling
  Gl := relabel G l : t
  sG0 : l (s G) = 0%nat
  edgeG : forall e : EdgeSet.elt,
          EdgeSet.In e (E G) -> VSet.In e..s (V G) /\ VSet.In e..t (V G)
  sG : VSet.In (s G) (V G)
  wG : forall x : VSet.elt,
       VSet.In x (V G) -> ∥ ∑ p : PathOf G (s G) x, ∥ 0 <= weight p ∥ ∥
  x : VSet.elt
  xin : VSet.In x (V Gl)
  p : PathOf G (s G) x
  h : ∥ 0 <= weight p ∥
  ============================
   (0 <= Z.of_nat (l x) - Z.of_nat 0)


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