(*==========================================================
       I- AND L-PRECONDITIONS, QUASI-HMAPS
==========================================================*)

(* For a unique insertion of a non nil dart
in a (future) qhmap: *)

Definition prec_I (m:fmap)(x:dart):=
  x <> nil /\ ~ exd m x .(* For correctness of functional link insertion, maybe incomplete, in a (future) qhmap: *)

Definition prec_Lq (m:fmap)(k:dim)(x y:dart) :=
  exd m x /\ exd m y /\ ~ succ m k x /\ ~ pred m k y.(* Quasi-map's topological invariant: in 2 parts *)

Fixpoint inv_qhmap(m:fmap){struct m}:Prop:=
  match m with
      V => True
    | I m0 x0 => inv_qhmap m0
         /\ prec_I m0 x0
    | L m0 k0 x0 y0 => inv_qhmap m0
         /\ prec_Lq m0 k0 x0 y0
  end.(* Definition of the qhmap type: (not used) *)

Definition qhmap:Set := {m:fmap | inv_qhmap m}.(* Projection of a qhmap to its fmap support: *)

Definition qhmap_to_fmap(q:qhmap):fmap:=
  match q with exist m _=> m end.

Lemma exd_not_nil : forall (m:fmap)(x:dart), inv_qhmap m -> exd m x -> x <> nil.