Goal:
  
  G : t
  HI : invariants
  HG : acyclic_no_loop
  x : VSet.elt
  inx : VSet.In x (V G)
  m : Z
  Hm : lsp (s G) x = Some m
  Hpos : 0 <= m
  ============================
   (exists n : Z,
      Some m = Some n /\ 0 <= n /\ Z.of_nat (to_label (Some m)) = n)


DEBUG:Going to execute:
eexists