(* FIXME
   Build an rmap that's identical to phi except where m has allocated. *)
Definition inflate_alloc: rmap.

Lemma approx_map_idem: forall n (lp: preds), preds_fmap (approx n) (approx n) (preds_fmap (approx n) (approx n) lp) = preds_fmap (approx n) (approx n) lp.