Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : V.t
  Vy : VSet.mem y (V G) = false
  e : n <= 0
  l : labelling
  Hl : correct_labelling G l
  k : Z
  Hk : lsp G x (s G) = Some k
  Hxs : n <= k
  p : SPath G (V G) x (s G)
  Hp : sweight p = k
  H : Z.of_nat (l x) + k <= Z.of_nat 0
  ============================
   (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