Goal:
  
  G : t
  invG : invariants G
  acG : acyclic_no_loop G
  l : labelling
  Hl : correct_labelling G l
  x : V.t
  k : nat
  d := Some (Z.of_nat (k + l x)) : option Z
  Hk : (lsp G x (s G) + d <= Some 0)%nbar
  Hl0 : l (s G) = 0%nat
  Hledge : forall e : EdgeSet.elt,
           EdgeSet.In e (E G) ->
           Z.of_nat (l e..s) + e..w <= Z.of_nat (l e..t)
  s : V.t
  w : Z
  t : V.t
  he : EdgeSet.In (s, w, t) (E G)
  u := to_label (lsp G x (s, w, t)..s + d)%nbar : nat
  ule : (l (s, w, t)..s <= u)%nat
  hs : VSet.In (s, w, t)..s (V G)
  ht : VSet.In (s, w, t)..t (V G)
  h : (lsp0 G (V G) x s + Some w <= lsp0 G (V G) x t)%nbar
  ============================
   (Z.of_nat u + (s, w, t)..w <=
    Z.of_nat
      (Nat.max (l (s, w, t)..t) (to_label (lsp G x (s, w, t)..t + d)%nbar)))


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrmove@1> $1 $2