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(*         *   The Coq Proof Assistant / The Coq Development Team       *)
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Require Import QArith_base Orders QOrderedType GenericMinMax.

(** * Maximum and Minimum of two rational numbers *)

Local Open Scope Q_scope.

(** [Qmin] and [Qmax] are obtained the usual way from [Qcompare]. *)

Definition Qmax := gmax Qcompare.
Definition Qmin := gmin Qcompare.

Module QHasMinMax <: HasMinMax Q_as_OT.
 Module QMM := GenericMinMax Q_as_OT.
 Definition max := Qmax.
 Definition min := Qmin.
 Definition max_l := QMM.max_l.
 Definition max_r := QMM.max_r.
 Definition min_l := QMM.min_l.
 Definition min_r := QMM.min_r.
End QHasMinMax.

Module Q.

(** We obtain hence all the generic properties of max and min. *)

Include MinMaxProperties Q_as_OT QHasMinMax.


(** * Properties specific to the [Q] domain *)

(** Compatibilities (consequences of monotonicity) *)

Lemma plus_max_distr_l : forall n m p, Qmax (p + n) (p + m) == p + Qmax n m.
Proof.
 intros. apply max_monotone.
 intros x x' Hx; rewrite Hx; auto with qarith.
 intros x x' Hx. apply Qplus_le_compat; q_order.
Qed.

Lemma plus_max_distr_r : forall n m p, Qmax (n + p) (m + p) == Qmax n m + p.
Proof.
 intros. rewrite (Qplus_comm n p), (Qplus_comm m p), (Qplus_comm _ p).
 apply plus_max_distr_l.
Qed.

Lemma plus_min_distr_l : forall n m p, Qmin (p + n) (p + m) == p + Qmin n m.
Proof.
 intros. apply min_monotone.
 intros x x' Hx; rewrite Hx; auto with qarith.
 intros x x' Hx. apply Qplus_le_compat; q_order.
Qed.

Lemma plus_min_distr_r : forall n m p, Qmin (n + p) (m + p) == Qmin n m + p.
Proof.
 intros. rewrite (Qplus_comm n p), (Qplus_comm m p), (Qplus_comm _ p).
 apply plus_min_distr_l.
Qed.

End Q.
