Goal:
    G : t  l : labelling  Hl : correct_labelling l  x : V.t  p : PathOf x x
  ============================
   (Z.of_nat (l x) + weight p <= Z.of_nat (l x) -> weight p <= 0)


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