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|
(************************************************************************)
(* v * The Coq Proof Assistant / The Coq Development Team *)
(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
(* \VV/ **************************************************************)
(* // * This file is distributed under the terms of the *)
(* * GNU Lesser General Public License Version 2.1 *)
(************************************************************************)
(*i $Id: Ndec.v 10739 2008-04-01 14:45:20Z herbelin $ i*)
Require Import Bool.
Require Import Sumbool.
Require Import Arith.
Require Import BinPos.
Require Import BinNat.
Require Import Pnat.
Require Import Nnat.
Require Import Ndigits.
(** A boolean equality over [N] *)
Fixpoint Peqb (p1 p2:positive) {struct p2} : bool :=
match p1, p2 with
| xH, xH => true
| xO p'1, xO p'2 => Peqb p'1 p'2
| xI p'1, xI p'2 => Peqb p'1 p'2
| _, _ => false
end.
Lemma Peqb_correct : forall p, Peqb p p = true.
Proof.
induction p; auto.
Qed.
Lemma Peqb_Pcompare : forall p p', Peqb p p' = true -> Pcompare p p' Eq = Eq.
Proof.
induction p; destruct p'; simpl; intros; try discriminate; auto.
Qed.
Lemma Peqb_complete : forall p p', Peqb p p' = true -> p = p'.
Proof.
intros.
apply Pcompare_Eq_eq.
apply Peqb_Pcompare; auto.
Qed.
Lemma Pcompare_Peqb : forall p p', Pcompare p p' Eq = Eq -> Peqb p p' = true.
Proof.
intros; rewrite <- (Pcompare_Eq_eq _ _ H).
apply Peqb_correct.
Qed.
Definition Neqb (a a':N) :=
match a, a' with
| N0, N0 => true
| Npos p, Npos p' => Peqb p p'
| _, _ => false
end.
Lemma Neqb_correct : forall n, Neqb n n = true.
Proof.
destruct n; trivial.
simpl; apply Peqb_correct.
Qed.
Lemma Neqb_Ncompare : forall n n', Neqb n n' = true -> Ncompare n n' = Eq.
Proof.
destruct n; destruct n'; simpl; intros; try discriminate; auto; apply Peqb_Pcompare; auto.
Qed.
Lemma Ncompare_Neqb : forall n n', Ncompare n n' = Eq -> Neqb n n' = true.
Proof.
intros; rewrite <- (Ncompare_Eq_eq _ _ H).
apply Neqb_correct.
Qed.
Lemma Neqb_complete : forall a a', Neqb a a' = true -> a = a'.
Proof.
intros.
apply Ncompare_Eq_eq.
apply Neqb_Ncompare; auto.
Qed.
Lemma Neqb_comm : forall a a', Neqb a a' = Neqb a' a.
Proof.
intros; apply bool_1; split; intros.
rewrite (Neqb_complete _ _ H); apply Neqb_correct.
rewrite (Neqb_complete _ _ H); apply Neqb_correct.
Qed.
Lemma Nxor_eq_true :
forall a a', Nxor a a' = N0 -> Neqb a a' = true.
Proof.
intros. rewrite (Nxor_eq a a' H). apply Neqb_correct.
Qed.
Lemma Nxor_eq_false :
forall a a' p, Nxor a a' = Npos p -> Neqb a a' = false.
Proof.
intros. elim (sumbool_of_bool (Neqb a a')). intro H0.
rewrite (Neqb_complete a a' H0) in H. rewrite (Nxor_nilpotent a') in H. discriminate H.
trivial.
Qed.
Lemma Nodd_not_double :
forall a,
Nodd a -> forall a0, Neqb (Ndouble a0) a = false.
Proof.
intros. elim (sumbool_of_bool (Neqb (Ndouble a0) a)). intro H0.
rewrite <- (Neqb_complete _ _ H0) in H.
unfold Nodd in H.
rewrite (Ndouble_bit0 a0) in H. discriminate H.
trivial.
Qed.
Lemma Nnot_div2_not_double :
forall a a0,
Neqb (Ndiv2 a) a0 = false -> Neqb a (Ndouble a0) = false.
Proof.
intros. elim (sumbool_of_bool (Neqb (Ndouble a0) a)). intro H0.
rewrite <- (Neqb_complete _ _ H0) in H. rewrite (Ndouble_div2 a0) in H.
rewrite (Neqb_correct a0) in H. discriminate H.
intro. rewrite Neqb_comm. assumption.
Qed.
Lemma Neven_not_double_plus_one :
forall a,
Neven a -> forall a0, Neqb (Ndouble_plus_one a0) a = false.
Proof.
intros. elim (sumbool_of_bool (Neqb (Ndouble_plus_one a0) a)). intro H0.
rewrite <- (Neqb_complete _ _ H0) in H.
unfold Neven in H.
rewrite (Ndouble_plus_one_bit0 a0) in H.
discriminate H.
trivial.
Qed.
Lemma Nnot_div2_not_double_plus_one :
forall a a0,
Neqb (Ndiv2 a) a0 = false -> Neqb (Ndouble_plus_one a0) a = false.
Proof.
intros. elim (sumbool_of_bool (Neqb a (Ndouble_plus_one a0))). intro H0.
rewrite (Neqb_complete _ _ H0) in H. rewrite (Ndouble_plus_one_div2 a0) in H.
rewrite (Neqb_correct a0) in H. discriminate H.
intro H0. rewrite Neqb_comm. assumption.
Qed.
Lemma Nbit0_neq :
forall a a',
Nbit0 a = false -> Nbit0 a' = true -> Neqb a a' = false.
Proof.
intros. elim (sumbool_of_bool (Neqb a a')). intro H1. rewrite (Neqb_complete _ _ H1) in H.
rewrite H in H0. discriminate H0.
trivial.
Qed.
Lemma Ndiv2_eq :
forall a a', Neqb a a' = true -> Neqb (Ndiv2 a) (Ndiv2 a') = true.
Proof.
intros. cut (a = a'). intros. rewrite H0. apply Neqb_correct.
apply Neqb_complete. exact H.
Qed.
Lemma Ndiv2_neq :
forall a a',
Neqb (Ndiv2 a) (Ndiv2 a') = false -> Neqb a a' = false.
Proof.
intros. elim (sumbool_of_bool (Neqb a a')). intro H0.
rewrite (Neqb_complete _ _ H0) in H. rewrite (Neqb_correct (Ndiv2 a')) in H. discriminate H.
trivial.
Qed.
Lemma Ndiv2_bit_eq :
forall a a',
Nbit0 a = Nbit0 a' -> Ndiv2 a = Ndiv2 a' -> a = a'.
Proof.
intros. apply Nbit_faithful. unfold eqf in |- *. destruct n.
rewrite Nbit0_correct. rewrite Nbit0_correct. assumption.
rewrite <- Ndiv2_correct. rewrite <- Ndiv2_correct.
rewrite H0. reflexivity.
Qed.
Lemma Ndiv2_bit_neq :
forall a a',
Neqb a a' = false ->
Nbit0 a = Nbit0 a' -> Neqb (Ndiv2 a) (Ndiv2 a') = false.
Proof.
intros. elim (sumbool_of_bool (Neqb (Ndiv2 a) (Ndiv2 a'))). intro H1.
rewrite (Ndiv2_bit_eq _ _ H0 (Neqb_complete _ _ H1)) in H.
rewrite (Neqb_correct a') in H. discriminate H.
trivial.
Qed.
Lemma Nneq_elim :
forall a a',
Neqb a a' = false ->
Nbit0 a = negb (Nbit0 a') \/
Neqb (Ndiv2 a) (Ndiv2 a') = false.
Proof.
intros. cut (Nbit0 a = Nbit0 a' \/ Nbit0 a = negb (Nbit0 a')).
intros. elim H0. intro. right. apply Ndiv2_bit_neq. assumption.
assumption.
intro. left. assumption.
case (Nbit0 a); case (Nbit0 a'); auto.
Qed.
Lemma Ndouble_or_double_plus_un :
forall a,
{a0 : N | a = Ndouble a0} + {a1 : N | a = Ndouble_plus_one a1}.
Proof.
intro. elim (sumbool_of_bool (Nbit0 a)). intro H. right. split with (Ndiv2 a).
rewrite (Ndiv2_double_plus_one a H). reflexivity.
intro H. left. split with (Ndiv2 a). rewrite (Ndiv2_double a H). reflexivity.
Qed.
(** A boolean order on [N] *)
Definition Nleb (a b:N) := leb (nat_of_N a) (nat_of_N b).
Lemma Nleb_Nle : forall a b, Nleb a b = true <-> Nle a b.
Proof.
intros; unfold Nle; rewrite nat_of_Ncompare.
unfold Nleb; apply leb_compare.
Qed.
Lemma Nleb_refl : forall a, Nleb a a = true.
Proof.
intro. unfold Nleb in |- *. apply leb_correct. apply le_n.
Qed.
Lemma Nleb_antisym :
forall a b, Nleb a b = true -> Nleb b a = true -> a = b.
Proof.
unfold Nleb in |- *. intros. rewrite <- (N_of_nat_of_N a). rewrite <- (N_of_nat_of_N b).
rewrite (le_antisym _ _ (leb_complete _ _ H) (leb_complete _ _ H0)). reflexivity.
Qed.
Lemma Nleb_trans :
forall a b c, Nleb a b = true -> Nleb b c = true -> Nleb a c = true.
Proof.
unfold Nleb in |- *. intros. apply leb_correct. apply le_trans with (m := nat_of_N b).
apply leb_complete. assumption.
apply leb_complete. assumption.
Qed.
Lemma Nleb_ltb_trans :
forall a b c,
Nleb a b = true -> Nleb c b = false -> Nleb c a = false.
Proof.
unfold Nleb in |- *. intros. apply leb_correct_conv. apply le_lt_trans with (m := nat_of_N b).
apply leb_complete. assumption.
apply leb_complete_conv. assumption.
Qed.
Lemma Nltb_leb_trans :
forall a b c,
Nleb b a = false -> Nleb b c = true -> Nleb c a = false.
Proof.
unfold Nleb in |- *. intros. apply leb_correct_conv. apply lt_le_trans with (m := nat_of_N b).
apply leb_complete_conv. assumption.
apply leb_complete. assumption.
Qed.
Lemma Nltb_trans :
forall a b c,
Nleb b a = false -> Nleb c b = false -> Nleb c a = false.
Proof.
unfold Nleb in |- *. intros. apply leb_correct_conv. apply lt_trans with (m := nat_of_N b).
apply leb_complete_conv. assumption.
apply leb_complete_conv. assumption.
Qed.
Lemma Nltb_leb_weak : forall a b:N, Nleb b a = false -> Nleb a b = true.
Proof.
unfold Nleb in |- *. intros. apply leb_correct. apply lt_le_weak.
apply leb_complete_conv. assumption.
Qed.
Lemma Nleb_double_mono :
forall a b,
Nleb a b = true -> Nleb (Ndouble a) (Ndouble b) = true.
Proof.
unfold Nleb in |- *. intros. rewrite nat_of_Ndouble. rewrite nat_of_Ndouble. apply leb_correct.
simpl in |- *. apply plus_le_compat. apply leb_complete. assumption.
apply plus_le_compat. apply leb_complete. assumption.
apply le_n.
Qed.
Lemma Nleb_double_plus_one_mono :
forall a b,
Nleb a b = true ->
Nleb (Ndouble_plus_one a) (Ndouble_plus_one b) = true.
Proof.
unfold Nleb in |- *. intros. rewrite nat_of_Ndouble_plus_one. rewrite nat_of_Ndouble_plus_one.
apply leb_correct. apply le_n_S. simpl in |- *. apply plus_le_compat. apply leb_complete.
assumption.
apply plus_le_compat. apply leb_complete. assumption.
apply le_n.
Qed.
Lemma Nleb_double_mono_conv :
forall a b,
Nleb (Ndouble a) (Ndouble b) = true -> Nleb a b = true.
Proof.
unfold Nleb in |- *. intros a b. rewrite nat_of_Ndouble. rewrite nat_of_Ndouble. intro.
apply leb_correct. apply (mult_S_le_reg_l 1). apply leb_complete. assumption.
Qed.
Lemma Nleb_double_plus_one_mono_conv :
forall a b,
Nleb (Ndouble_plus_one a) (Ndouble_plus_one b) = true ->
Nleb a b = true.
Proof.
unfold Nleb in |- *. intros a b. rewrite nat_of_Ndouble_plus_one. rewrite nat_of_Ndouble_plus_one.
intro. apply leb_correct. apply (mult_S_le_reg_l 1). apply le_S_n. apply leb_complete.
assumption.
Qed.
Lemma Nltb_double_mono :
forall a b,
Nleb a b = false -> Nleb (Ndouble a) (Ndouble b) = false.
Proof.
intros. elim (sumbool_of_bool (Nleb (Ndouble a) (Ndouble b))). intro H0.
rewrite (Nleb_double_mono_conv _ _ H0) in H. discriminate H.
trivial.
Qed.
Lemma Nltb_double_plus_one_mono :
forall a b,
Nleb a b = false ->
Nleb (Ndouble_plus_one a) (Ndouble_plus_one b) = false.
Proof.
intros. elim (sumbool_of_bool (Nleb (Ndouble_plus_one a) (Ndouble_plus_one b))). intro H0.
rewrite (Nleb_double_plus_one_mono_conv _ _ H0) in H. discriminate H.
trivial.
Qed.
Lemma Nltb_double_mono_conv :
forall a b,
Nleb (Ndouble a) (Ndouble b) = false -> Nleb a b = false.
Proof.
intros. elim (sumbool_of_bool (Nleb a b)). intro H0. rewrite (Nleb_double_mono _ _ H0) in H.
discriminate H.
trivial.
Qed.
Lemma Nltb_double_plus_one_mono_conv :
forall a b,
Nleb (Ndouble_plus_one a) (Ndouble_plus_one b) = false ->
Nleb a b = false.
Proof.
intros. elim (sumbool_of_bool (Nleb a b)). intro H0.
rewrite (Nleb_double_plus_one_mono _ _ H0) in H. discriminate H.
trivial.
Qed.
(* An alternate [min] function over [N] *)
Definition Nmin' (a b:N) := if Nleb a b then a else b.
Lemma Nmin_Nmin' : forall a b, Nmin a b = Nmin' a b.
Proof.
unfold Nmin, Nmin', Nleb; intros.
rewrite nat_of_Ncompare.
generalize (leb_compare (nat_of_N a) (nat_of_N b));
destruct (nat_compare (nat_of_N a) (nat_of_N b));
destruct (leb (nat_of_N a) (nat_of_N b)); intuition.
lapply H1; intros; discriminate.
lapply H1; intros; discriminate.
Qed.
Lemma Nmin_choice : forall a b, {Nmin a b = a} + {Nmin a b = b}.
Proof.
unfold Nmin in *; intros; destruct (Ncompare a b); auto.
Qed.
Lemma Nmin_le_1 : forall a b, Nleb (Nmin a b) a = true.
Proof.
intros; rewrite Nmin_Nmin'.
unfold Nmin'; elim (sumbool_of_bool (Nleb a b)). intro H. rewrite H.
apply Nleb_refl.
intro H. rewrite H. apply Nltb_leb_weak. assumption.
Qed.
Lemma Nmin_le_2 : forall a b, Nleb (Nmin a b) b = true.
Proof.
intros; rewrite Nmin_Nmin'.
unfold Nmin'; elim (sumbool_of_bool (Nleb a b)). intro H. rewrite H. assumption.
intro H. rewrite H. apply Nleb_refl.
Qed.
Lemma Nmin_le_3 :
forall a b c, Nleb a (Nmin b c) = true -> Nleb a b = true.
Proof.
intros; rewrite Nmin_Nmin' in *.
unfold Nmin' in *; elim (sumbool_of_bool (Nleb b c)). intro H0. rewrite H0 in H.
assumption.
intro H0. rewrite H0 in H. apply Nltb_leb_weak. apply Nleb_ltb_trans with (b := c); assumption.
Qed.
Lemma Nmin_le_4 :
forall a b c, Nleb a (Nmin b c) = true -> Nleb a c = true.
Proof.
intros; rewrite Nmin_Nmin' in *.
unfold Nmin' in *; elim (sumbool_of_bool (Nleb b c)). intro H0. rewrite H0 in H.
apply Nleb_trans with (b := b); assumption.
intro H0. rewrite H0 in H. assumption.
Qed.
Lemma Nmin_le_5 :
forall a b c,
Nleb a b = true -> Nleb a c = true -> Nleb a (Nmin b c) = true.
Proof.
intros. elim (Nmin_choice b c). intro H1. rewrite H1. assumption.
intro H1. rewrite H1. assumption.
Qed.
Lemma Nmin_lt_3 :
forall a b c, Nleb (Nmin b c) a = false -> Nleb b a = false.
Proof.
intros; rewrite Nmin_Nmin' in *.
unfold Nmin' in *. intros. elim (sumbool_of_bool (Nleb b c)). intro H0. rewrite H0 in H.
assumption.
intro H0. rewrite H0 in H. apply Nltb_trans with (b := c); assumption.
Qed.
Lemma Nmin_lt_4 :
forall a b c, Nleb (Nmin b c) a = false -> Nleb c a = false.
Proof.
intros; rewrite Nmin_Nmin' in *.
unfold Nmin' in *. elim (sumbool_of_bool (Nleb b c)). intro H0. rewrite H0 in H.
apply Nltb_leb_trans with (b := b); assumption.
intro H0. rewrite H0 in H. assumption.
Qed.
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