Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : V.t
  Vy : ~ VSet.In y (V G)
  G' := G' (s G) x (Z.succ (- n - n)) : t
  e : y = y
  Hy : x <> y
  nneg : n <= 0
  n0 : x <> y
  Hxs : lsp G x (s G) = None
  Vx : VSet.In x (V G)
  H : x <> s G
  X : correct_labelling G (fun x : V.t => to_label (lsp G' (s G) x))
  HI' : invariants G'
  HG' : acyclic_no_loop G'
  XX : correct_labelling G
         (fun z : V.t =>
          if is_left (V.eq_dec z y)
          then Z.to_nat (- n)
          else to_label (lsp G' (s G) z))
  kx : Z
  Hkx : lsp0 G' (V G) (s G) x = Some kx
  YY : Z.succ (- n - n) + 0 <= kx
  Hle : 0 + n <= Z.of_nat (Z.to_nat (- n))
  H0 : kx < 0
  ============================
   False


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