Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : VSet.elt
  Vy : VSet.In y (V G)
  m : Z
  p : SPath G (V G) x y
  Hp : sweight p = m
  l : labelling
  Hl : correct_labelling G l
  Hle : n <= m
  XX : Z.of_nat (l x) + m <= Z.of_nat (l y)
  ============================
   (Z.of_nat (l x) + n <= Z.of_nat (l y))


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