Corollary paco0_mult: forall r,
  paco0 gf (paco0 gf r) <0= paco0 gf r.

(* Specifications: *)
Theorem paco0_fold: forall r, gf (upaco0 gf r) <0= paco0 gf r.
Theorem paco0_unfold: forall (MON: monotone0 gf) r, paco0 gf r <0= gf (upaco0 gf r).