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(***********************************************************************)
(* v * The Coq Proof Assistant / The Coq Development Team *)
(* <O___,, * INRIA-Rocquencourt & LRI-CNRS-Orsay *)
(* \VV/ *************************************************************)
(* // * This file is distributed under the terms of the *)
(* * GNU Lesser General Public License Version 2.1 *)
(***********************************************************************)
(* Finite sets library.
* Authors: Pierre Letouzey and Jean-Christophe Filliâtre
* Institution: LRI, CNRS UMR 8623 - Université Paris Sud
* 91405 Orsay, France *)
Require Import Orders NPeano POrderedType NArith
ZArith RelationPairs EqualitiesFacts.
(** * Examples of Ordered Type structures. *)
(** Ordered Type for [nat], [Positive], [N], [Z] with the usual order. *)
Module Nat_as_OT := NPeano.Nat.
Module Positive_as_OT := POrderedType.Positive_as_OT.
Module N_as_OT := BinNat.N.
Module Z_as_OT := BinInt.Z.
(** An OrderedType can now directly be seen as a DecidableType *)
Module OT_as_DT (O:OrderedType) <: DecidableType := O.
(** (Usual) Decidable Type for [nat], [positive], [N], [Z] *)
Module Nat_as_DT <: UsualDecidableType := Nat_as_OT.
Module Positive_as_DT <: UsualDecidableType := Positive_as_OT.
Module N_as_DT <: UsualDecidableType := N_as_OT.
Module Z_as_DT <: UsualDecidableType := Z_as_OT.
(** From two ordered types, we can build a new OrderedType
over their cartesian product, using the lexicographic order. *)
Module PairOrderedType(O1 O2:OrderedType) <: OrderedType.
Include PairDecidableType O1 O2.
Definition lt :=
(relation_disjunction (O1.lt @@1) (O1.eq * O2.lt))%signature.
Instance lt_strorder : StrictOrder lt.
Proof.
split.
(* irreflexive *)
intros (x1,x2); compute. destruct 1.
apply (StrictOrder_Irreflexive x1); auto.
apply (StrictOrder_Irreflexive x2); intuition.
(* transitive *)
intros (x1,x2) (y1,y2) (z1,z2). compute. intuition.
left; etransitivity; eauto.
left. setoid_replace z1 with y1; auto with relations.
left; setoid_replace x1 with y1; auto with relations.
right; split; etransitivity; eauto.
Qed.
Instance lt_compat : Proper (eq==>eq==>iff) lt.
Proof.
compute.
intros (x1,x2) (x1',x2') (X1,X2) (y1,y2) (y1',y2') (Y1,Y2).
rewrite X1,X2,Y1,Y2; intuition.
Qed.
Definition compare x y :=
match O1.compare (fst x) (fst y) with
| Eq => O2.compare (snd x) (snd y)
| Lt => Lt
| Gt => Gt
end.
Lemma compare_spec : forall x y, CompSpec eq lt x y (compare x y).
Proof.
intros (x1,x2) (y1,y2); unfold compare; simpl.
destruct (O1.compare_spec x1 y1); try (constructor; compute; auto).
destruct (O2.compare_spec x2 y2); constructor; compute; auto with relations.
Qed.
End PairOrderedType.
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