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
  ============================
   (correct_labelling G r)


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrcase@0> $1 $2