Goal:
  
  G : t
  HI : invariants
  HG : acyclic_no_loop
  x : VSet.elt
  Hx : VSet.In x (V G)
  n : Z
  ============================
   (lsp x (s G) = None -> None = Some n -> n <= 0)


DEBUG:Going to execute:
<coq-core.plugins.ltac::intro@1> $1