# Missing definitions/lemmas

Require Export Reals.
Require Export ZArith.
Require Export Fcore_Zaux.

Section Rmissing.

Theorem Rle_0_minus :
forall x y, (x <= y)%R -> (0 <= y - x)%R.
Proof.
intros.
apply Rge_le.
apply Rge_minus.
now apply Rle_ge.
Qed.

Theorem Rabs_eq_Rabs :
forall x y : R,
Rabs x = Rabs y -> x = y \/ x = Ropp y.
Proof.
intros x y H.
unfold Rabs in H.
destruct (Rcase_abs x) as [_|_].
assert (H' := f_equal Ropp H).
rewrite Ropp_involutive in H'.
rewrite H'.
destruct (Rcase_abs y) as [_|_].
left.
apply Ropp_involutive.
now right.
rewrite H.
now destruct (Rcase_abs y) as [_|_] ; [right|left].
Qed.

Theorem Rabs_minus_le:
forall x y : R,
(0 <= y)%R -> (y <= 2*x)%R ->
(Rabs (x-y) <= x)%R.
Proof.
intros x y Hx Hy.
unfold Rabs; case (Rcase_abs (x - y)); intros H.
apply Rplus_le_reg_l with x; ring_simplify; assumption.
apply Rplus_le_reg_l with (-x)%R; ring_simplify.
auto with real.
Qed.

Theorem Rplus_eq_reg_r :
forall r r1 r2 : R,
(r1 + r = r2 + r)%R -> (r1 = r2)%R.
Proof.
intros r r1 r2 H.
apply Rplus_eq_reg_l with r.
now rewrite 2!(Rplus_comm r).
Qed.

Theorem Rplus_lt_reg_l :
forall r r1 r2 : R,
(r + r1 < r + r2)%R -> (r1 < r2)%R.
Proof.
intros.
solve [ apply Rplus_lt_reg_l with (1 := H) |
apply Rplus_lt_reg_r with (1 := H) ].
Qed.

Theorem Rplus_lt_reg_r :
forall r r1 r2 : R,
(r1 + r < r2 + r)%R -> (r1 < r2)%R.
Proof.
intros.
apply Rplus_lt_reg_l with r.
now rewrite 2!(Rplus_comm r).
Qed.

Theorem Rplus_le_reg_r :
forall r r1 r2 : R,
(r1 + r <= r2 + r)%R -> (r1 <= r2)%R.
Proof.
intros.
apply Rplus_le_reg_l with r.
now rewrite 2!(Rplus_comm r).
Qed.

Theorem Rmult_lt_reg_r :
forall r r1 r2 : R, (0 < r)%R ->
(r1 * r < r2 * r)%R -> (r1 < r2)%R.
Proof.
intros.
apply Rmult_lt_reg_l with r.
exact H.
now rewrite 2!(Rmult_comm r).
Qed.

Theorem Rmult_le_reg_r :
forall r r1 r2 : R, (0 < r)%R ->
(r1 * r <= r2 * r)%R -> (r1 <= r2)%R.
Proof.
intros.
apply Rmult_le_reg_l with r.
exact H.
now rewrite 2!(Rmult_comm r).
Qed.

Theorem Rmult_lt_compat :
forall r1 r2 r3 r4,
(0 <= r1)%R -> (0 <= r3)%R -> (r1 < r2)%R -> (r3 < r4)%R ->
(r1 * r3 < r2 * r4)%R.
Proof.
intros r1 r2 r3 r4 Pr1 Pr3 H12 H34.
apply Rle_lt_trans with (r1 * r4)%R.
- apply Rmult_le_compat_l.
+ exact Pr1.
+ now apply Rlt_le.
- apply Rmult_lt_compat_r.
+ now apply Rle_lt_trans with r3.
+ exact H12.
Qed.

Theorem Rmult_eq_reg_r :
forall r r1 r2 : R, (r1 * r)%R = (r2 * r)%R ->
r <> 0%R -> r1 = r2.
Proof.
intros r r1 r2 H1 H2.
apply Rmult_eq_reg_l with r.
now rewrite 2!(Rmult_comm r).
exact H2.
Qed.

Theorem Rmult_minus_distr_r :
forall r r1 r2 : R,
((r1 - r2) * r = r1 * r - r2 * r)%R.
Proof.
intros r r1 r2.
rewrite <- 3!(Rmult_comm r).
apply Rmult_minus_distr_l.
Qed.

Lemma Rmult_neq_reg_r: forall r1 r2 r3:R, (r2 * r1 <> r3 * r1)%R -> r2 <> r3.
intros r1 r2 r3 H1 H2.
apply H1; rewrite H2; ring.
Qed.

Lemma Rmult_neq_compat_r: forall r1 r2 r3:R, (r1 <> 0)%R -> (r2 <> r3)%R
-> (r2 *r1 <> r3*r1)%R.
intros r1 r2 r3 H H1 H2.
now apply H1, Rmult_eq_reg_r with r1.
Qed.

Theorem Rmult_min_distr_r :
forall r r1 r2 : R,
(0 <= r)%R ->
(Rmin r1 r2 * r)%R = Rmin (r1 * r) (r2 * r).
Proof.
intros r r1 r2 [Hr|Hr].
unfold Rmin.
destruct (Rle_dec r1 r2) as [H1|H1] ;
destruct (Rle_dec (r1 * r) (r2 * r)) as [H2|H2] ;
try easy.
apply (f_equal (fun x => Rmult x r)).
apply Rle_antisym.
exact H1.
apply Rmult_le_reg_r with (1 := Hr).
apply Rlt_le.
now apply Rnot_le_lt.
apply Rle_antisym.
apply Rmult_le_compat_r.
now apply Rlt_le.
apply Rlt_le.
now apply Rnot_le_lt.
exact H2.
rewrite <- Hr.
rewrite 3!Rmult_0_r.
unfold Rmin.
destruct (Rle_dec 0 0) as [H0|H0].
easy.
elim H0.
apply Rle_refl.
Qed.

Theorem Rmult_min_distr_l :
forall r r1 r2 : R,
(0 <= r)%R ->
(r * Rmin r1 r2)%R = Rmin (r * r1) (r * r2).
Proof.
intros r r1 r2 Hr.
rewrite 3!(Rmult_comm r).
now apply Rmult_min_distr_r.
Qed.

Lemma Rmin_opp: forall x y, (Rmin (-x) (-y) = - Rmax x y)%R.
Proof.
intros x y.
apply Rmax_case_strong; intros H.
rewrite Rmin_left; trivial.
now apply Ropp_le_contravar.
rewrite Rmin_right; trivial.
now apply Ropp_le_contravar.
Qed.

Lemma Rmax_opp: forall x y, (Rmax (-x) (-y) = - Rmin x y)%R.
Proof.
intros x y.
apply Rmin_case_strong; intros H.
rewrite Rmax_left; trivial.
now apply Ropp_le_contravar.
rewrite Rmax_right; trivial.
now apply Ropp_le_contravar.
Qed.

Theorem exp_le :
forall x y : R,
(x <= y)%R -> (exp x <= exp y)%R.
Proof.
intros x y [H|H].
apply Rlt_le.
now apply exp_increasing.
rewrite H.
apply Rle_refl.
Qed.

Theorem Rinv_lt :
forall x y,
(0 < x)%R -> (x < y)%R -> (/y < /x)%R.
Proof.
intros x y Hx Hxy.
apply Rinv_lt_contravar.
apply Rmult_lt_0_compat.
exact Hx.
now apply Rlt_trans with x.
exact Hxy.
Qed.

Theorem Rinv_le :
forall x y,
(0 < x)%R -> (x <= y)%R -> (/y <= /x)%R.
Proof.
intros x y Hx Hxy.
apply Rle_Rinv.
exact Hx.
now apply Rlt_le_trans with x.
exact Hxy.
Qed.

Theorem sqrt_ge_0 :
forall x : R,
(0 <= sqrt x)%R.
Proof.
intros x.
unfold sqrt.
destruct (Rcase_abs x) as [_|H].
apply Rle_refl.
apply Rsqrt_positivity.
Qed.

Lemma sqrt_neg : forall x, (x <= 0)%R -> (sqrt x = 0)%R.
Proof.
intros x Npx.
destruct (Req_dec x 0) as [Zx|Nzx].
- (* x = 0 *)
rewrite Zx.
exact sqrt_0.
- (* x < 0 *)
unfold sqrt.
destruct Rcase_abs.
+ reflexivity.
+ casetype False.
now apply Nzx, Rle_antisym; [|apply Rge_le].
Qed.

Theorem Rabs_le :
forall x y,
(-y <= x <= y)%R -> (Rabs x <= y)%R.
Proof.
intros x y (Hyx,Hxy).
unfold Rabs.
case Rcase_abs ; intros Hx.
apply Ropp_le_cancel.
now rewrite Ropp_involutive.
exact Hxy.
Qed.

Theorem Rabs_le_inv :
forall x y,
(Rabs x <= y)%R -> (-y <= x <= y)%R.
Proof.
intros x y Hxy.
split.
apply Rle_trans with (- Rabs x)%R.
now apply Ropp_le_contravar.
apply Ropp_le_cancel.
rewrite Ropp_involutive, <- Rabs_Ropp.
apply RRle_abs.
apply Rle_trans with (2 := Hxy).
apply RRle_abs.
Qed.

Theorem Rabs_ge :
forall x y,
(y <= -x \/ x <= y)%R -> (x <= Rabs y)%R.
Proof.
intros x y [Hyx|Hxy].
apply Rle_trans with (-y)%R.
apply Ropp_le_cancel.
now rewrite Ropp_involutive.
rewrite <- Rabs_Ropp.
apply RRle_abs.
apply Rle_trans with (1 := Hxy).
apply RRle_abs.
Qed.

Theorem Rabs_ge_inv :
forall x y,
(x <= Rabs y)%R -> (y <= -x \/ x <= y)%R.
Proof.
intros x y.
unfold Rabs.
case Rcase_abs ; intros Hy Hxy.
left.
apply Ropp_le_cancel.
now rewrite Ropp_involutive.
now right.
Qed.

Theorem Rabs_lt :
forall x y,
(-y < x < y)%R -> (Rabs x < y)%R.
Proof.
intros x y (Hyx,Hxy).
now apply Rabs_def1.
Qed.

Theorem Rabs_lt_inv :
forall x y,
(Rabs x < y)%R -> (-y < x < y)%R.
Proof.
intros x y H.
now split ; eapply Rabs_def2.
Qed.

Theorem Rabs_gt :
forall x y,
(y < -x \/ x < y)%R -> (x < Rabs y)%R.
Proof.
intros x y [Hyx|Hxy].
rewrite <- Rabs_Ropp.
apply Rlt_le_trans with (Ropp y).
apply Ropp_lt_cancel.
now rewrite Ropp_involutive.
apply RRle_abs.
apply Rlt_le_trans with (1 := Hxy).
apply RRle_abs.
Qed.

Theorem Rabs_gt_inv :
forall x y,
(x < Rabs y)%R -> (y < -x \/ x < y)%R.
Proof.
intros x y.
unfold Rabs.
case Rcase_abs ; intros Hy Hxy.
left.
apply Ropp_lt_cancel.
now rewrite Ropp_involutive.
now right.
Qed.

End Rmissing.

Section Z2R.

Z2R function (Z -> R)
Fixpoint P2R (p : positive) :=
match p with
| xH => 1%R
| xO xH => 2%R
| xO t => (2 * P2R t)%R
| xI xH => 3%R
| xI t => (1 + 2 * P2R t)%R
end.

Definition Z2R n :=
match n with
| Zpos p => P2R p
| Zneg p => Ropp (P2R p)
| Z0 => 0%R
end.

Theorem P2R_INR :
forall n, P2R n = INR (nat_of_P n).
Proof.
induction n ; simpl ; try (
rewrite IHn ;
rewrite <- (mult_INR 2) ;
rewrite <- (nat_of_P_mult_morphism 2) ;
change (2 * n)%positive with (xO n)).
xI *)rewrite (Rplus_comm 1).
change (nat_of_P (xO n)) with (Pmult_nat n 2).
case n ; intros ; simpl ; try apply refl_equal.
case (Pmult_nat p 4) ; intros ; try apply refl_equal.
rewrite Rplus_0_l.
apply refl_equal.
apply Rplus_comm.
xO *)case n ; intros ; apply refl_equal.
xH *)apply refl_equal.
Qed.

Theorem Z2R_IZR :
forall n, Z2R n = IZR n.
Proof.
intro.
case n ; intros ; unfold Z2R.
apply refl_equal.
rewrite <- positive_nat_Z, <- INR_IZR_INZ.
apply P2R_INR.
change (IZR (Zneg p)) with (Ropp (IZR (Zpos p))).
apply Ropp_eq_compat.
rewrite <- positive_nat_Z, <- INR_IZR_INZ.
apply P2R_INR.
Qed.

Theorem Z2R_opp :
forall n, Z2R (-n) = (- Z2R n)%R.
Proof.
intros.
repeat rewrite Z2R_IZR.
apply Ropp_Ropp_IZR.
Qed.

Theorem Z2R_plus :
forall m n, (Z2R (m + n) = Z2R m + Z2R n)%R.
Proof.
intros.
repeat rewrite Z2R_IZR.
apply plus_IZR.
Qed.

Theorem minus_IZR :
forall n m : Z,
IZR (n - m) = (IZR n - IZR m)%R.
Proof.
intros.
unfold Zminus.
rewrite plus_IZR.
rewrite Ropp_Ropp_IZR.
apply refl_equal.
Qed.

Theorem Z2R_minus :
forall m n, (Z2R (m - n) = Z2R m - Z2R n)%R.
Proof.
intros.
repeat rewrite Z2R_IZR.
apply minus_IZR.
Qed.

Theorem Z2R_mult :
forall m n, (Z2R (m * n) = Z2R m * Z2R n)%R.
Proof.
intros.
repeat rewrite Z2R_IZR.
apply mult_IZR.
Qed.

Theorem le_Z2R :
forall m n, (Z2R m <= Z2R n)%R -> (m <= n)%Z.
Proof.
intros m n.
repeat rewrite Z2R_IZR.
apply le_IZR.
Qed.

Theorem Z2R_le :
forall m n, (m <= n)%Z -> (Z2R m <= Z2R n)%R.
Proof.
intros m n.
repeat rewrite Z2R_IZR.
apply IZR_le.
Qed.

Theorem lt_Z2R :
forall m n, (Z2R m < Z2R n)%R -> (m < n)%Z.
Proof.
intros m n.
repeat rewrite Z2R_IZR.
apply lt_IZR.
Qed.

Theorem Z2R_lt :
forall m n, (m < n)%Z -> (Z2R m < Z2R n)%R.
Proof.
intros m n.
repeat rewrite Z2R_IZR.
apply IZR_lt.
Qed.

Theorem Z2R_le_lt :
forall m n p, (m <= n < p)%Z -> (Z2R m <= Z2R n < Z2R p)%R.
Proof.
intros m n p (H1, H2).
split.
now apply Z2R_le.
now apply Z2R_lt.
Qed.

Theorem le_lt_Z2R :
forall m n p, (Z2R m <= Z2R n < Z2R p)%R -> (m <= n < p)%Z.
Proof.
intros m n p (H1, H2).
split.
now apply le_Z2R.
now apply lt_Z2R.
Qed.

Theorem eq_Z2R :
forall m n, (Z2R m = Z2R n)%R -> (m = n)%Z.
Proof.
intros m n H.
apply eq_IZR.
now rewrite <- 2!Z2R_IZR.
Qed.

Theorem neq_Z2R :
forall m n, (Z2R m <> Z2R n)%R -> (m <> n)%Z.
Proof.
intros m n H H'.
apply H.
now apply f_equal.
Qed.

Theorem Z2R_neq :
forall m n, (m <> n)%Z -> (Z2R m <> Z2R n)%R.
Proof.
intros m n.
repeat rewrite Z2R_IZR.
apply IZR_neq.
Qed.

Theorem Z2R_abs :
forall z, Z2R (Zabs z) = Rabs (Z2R z).
Proof.
intros.
repeat rewrite Z2R_IZR.
now rewrite Rabs_Zabs.
Qed.

End Z2R.

Decidable comparison on reals
Section Rcompare.

Definition Rcompare x y :=
match total_order_T x y with
| inleft (left _) => Lt
| inleft (right _) => Eq
| inright _ => Gt
end.

Inductive Rcompare_prop (x y : R) : comparison -> Prop :=
| Rcompare_Lt_ : (x < y)%R -> Rcompare_prop x y Lt
| Rcompare_Eq_ : x = y -> Rcompare_prop x y Eq
| Rcompare_Gt_ : (y < x)%R -> Rcompare_prop x y Gt.

Theorem Rcompare_spec :
forall x y, Rcompare_prop x y (Rcompare x y).
Proof.
intros x y.
unfold Rcompare.
now destruct (total_order_T x y) as [[H|H]|H] ; constructor.
Qed.

Global Opaque Rcompare.

Theorem Rcompare_Lt :
forall x y,
(x < y)%R -> Rcompare x y = Lt.
Proof.
intros x y H.
case Rcompare_spec ; intro H'.
easy.
rewrite H' in H.
elim (Rlt_irrefl _ H).
elim (Rlt_irrefl x).
now apply Rlt_trans with y.
Qed.

Theorem Rcompare_Lt_inv :
forall x y,
Rcompare x y = Lt -> (x < y)%R.
Proof.
intros x y.
now case Rcompare_spec.
Qed.

Theorem Rcompare_not_Lt :
forall x y,
(y <= x)%R -> Rcompare x y <> Lt.
Proof.
intros x y H1 H2.
apply Rle_not_lt with (1 := H1).
now apply Rcompare_Lt_inv.
Qed.

Theorem Rcompare_not_Lt_inv :
forall x y,
Rcompare x y <> Lt -> (y <= x)%R.
Proof.
intros x y H.
apply Rnot_lt_le.
now apply Rcompare_Lt.
Qed.

Theorem Rcompare_Eq :
forall x y,
x = y -> Rcompare x y = Eq.
Proof.
intros x y H.
rewrite H.
now case Rcompare_spec ; intro H' ; try elim (Rlt_irrefl _ H').
Qed.

Theorem Rcompare_Eq_inv :
forall x y,
Rcompare x y = Eq -> x = y.
Proof.
intros x y.
now case Rcompare_spec.
Qed.

Theorem Rcompare_Gt :
forall x y,
(y < x)%R -> Rcompare x y = Gt.
Proof.
intros x y H.
case Rcompare_spec ; intro H'.
elim (Rlt_irrefl x).
now apply Rlt_trans with y.
rewrite H' in H.
elim (Rlt_irrefl _ H).
easy.
Qed.

Theorem Rcompare_Gt_inv :
forall x y,
Rcompare x y = Gt -> (y < x)%R.
Proof.
intros x y.
now case Rcompare_spec.
Qed.

Theorem Rcompare_not_Gt :
forall x y,
(x <= y)%R -> Rcompare x y <> Gt.
Proof.
intros x y H1 H2.
apply Rle_not_lt with (1 := H1).
now apply Rcompare_Gt_inv.
Qed.

Theorem Rcompare_not_Gt_inv :
forall x y,
Rcompare x y <> Gt -> (x <= y)%R.
Proof.
intros x y H.
apply Rnot_lt_le.
now apply Rcompare_Gt.
Qed.

Theorem Rcompare_Z2R :
forall x y, Rcompare (Z2R x) (Z2R y) = Zcompare x y.
Proof.
intros x y.
case Rcompare_spec ; intros H ; apply sym_eq.
apply Zcompare_Lt.
now apply lt_Z2R.
apply Zcompare_Eq.
now apply eq_Z2R.
apply Zcompare_Gt.
now apply lt_Z2R.
Qed.

Theorem Rcompare_sym :
forall x y,
Rcompare x y = CompOpp (Rcompare y x).
Proof.
intros x y.
destruct (Rcompare_spec y x) as [H|H|H].
now apply Rcompare_Gt.
now apply Rcompare_Eq.
now apply Rcompare_Lt.
Qed.

Theorem Rcompare_plus_r :
forall z x y,
Rcompare (x + z) (y + z) = Rcompare x y.
Proof.
intros z x y.
destruct (Rcompare_spec x y) as [H|H|H].
apply Rcompare_Lt.
now apply Rplus_lt_compat_r.
apply Rcompare_Eq.
now rewrite H.
apply Rcompare_Gt.
now apply Rplus_lt_compat_r.
Qed.

Theorem Rcompare_plus_l :
forall z x y,
Rcompare (z + x) (z + y) = Rcompare x y.
Proof.
intros z x y.
rewrite 2!(Rplus_comm z).
apply Rcompare_plus_r.
Qed.

Theorem Rcompare_mult_r :
forall z x y,
(0 < z)%R ->
Rcompare (x * z) (y * z) = Rcompare x y.
Proof.
intros z x y Hz.
destruct (Rcompare_spec x y) as [H|H|H].
apply Rcompare_Lt.
now apply Rmult_lt_compat_r.
apply Rcompare_Eq.
now rewrite H.
apply Rcompare_Gt.
now apply Rmult_lt_compat_r.
Qed.

Theorem Rcompare_mult_l :
forall z x y,
(0 < z)%R ->
Rcompare (z * x) (z * y) = Rcompare x y.
Proof.
intros z x y.
rewrite 2!(Rmult_comm z).
apply Rcompare_mult_r.
Qed.

Theorem Rcompare_middle :
forall x d u,
Rcompare (x - d) (u - x) = Rcompare x ((d + u) / 2).
Proof.
intros x d u.
rewrite <- (Rcompare_plus_r (- x / 2 - d / 2) x).
rewrite <- (Rcompare_mult_r (/2) (x - d)).
field_simplify (x + (- x / 2 - d / 2))%R.
now field_simplify ((d + u) / 2 + (- x / 2 - d / 2))%R.
apply Rinv_0_lt_compat.
now apply (Z2R_lt 0 2).
Qed.

Theorem Rcompare_half_l :
forall x y, Rcompare (x / 2) y = Rcompare x (2 * y).
Proof.
intros x y.
rewrite <- (Rcompare_mult_r 2%R).
unfold Rdiv.
rewrite Rmult_assoc, Rinv_l, Rmult_1_r.
now rewrite Rmult_comm.
now apply (Z2R_neq 2 0).
now apply (Z2R_lt 0 2).
Qed.

Theorem Rcompare_half_r :
forall x y, Rcompare x (y / 2) = Rcompare (2 * x) y.
Proof.
intros x y.
rewrite <- (Rcompare_mult_r 2%R).
unfold Rdiv.
rewrite Rmult_assoc, Rinv_l, Rmult_1_r.
now rewrite Rmult_comm.
now apply (Z2R_neq 2 0).
now apply (Z2R_lt 0 2).
Qed.

Theorem Rcompare_sqr :
forall x y,
(0 <= x)%R -> (0 <= y)%R ->
Rcompare (x * x) (y * y) = Rcompare x y.
Proof.
intros x y Hx Hy.
destruct (Rcompare_spec x y) as [H|H|H].
apply Rcompare_Lt.
now apply Rsqr_incrst_1.
rewrite H.
now apply Rcompare_Eq.
apply Rcompare_Gt.
now apply Rsqr_incrst_1.
Qed.

Theorem Rmin_compare :
forall x y,
Rmin x y = match Rcompare x y with Lt => x | Eq => x | Gt => y end.
Proof.
intros x y.
unfold Rmin.
destruct (Rle_dec x y) as [[Hx|Hx]|Hx].
now rewrite Rcompare_Lt.
now rewrite Rcompare_Eq.
rewrite Rcompare_Gt.
easy.
now apply Rnot_le_lt.
Qed.

End Rcompare.

Section Rle_bool.

Definition Rle_bool x y :=
match Rcompare x y with
| Gt => false
| _ => true
end.

Inductive Rle_bool_prop (x y : R) : bool -> Prop :=
| Rle_bool_true_ : (x <= y)%R -> Rle_bool_prop x y true
| Rle_bool_false_ : (y < x)%R -> Rle_bool_prop x y false.

Theorem Rle_bool_spec :
forall x y, Rle_bool_prop x y (Rle_bool x y).
Proof.
intros x y.
unfold Rle_bool.
case Rcompare_spec ; constructor.
now apply Rlt_le.
rewrite H.
apply Rle_refl.
exact H.
Qed.

Theorem Rle_bool_true :
forall x y,
(x <= y)%R -> Rle_bool x y = true.
Proof.
intros x y Hxy.
case Rle_bool_spec ; intros H.
apply refl_equal.
elim (Rlt_irrefl x).
now apply Rle_lt_trans with y.
Qed.

Theorem Rle_bool_false :
forall x y,
(y < x)%R -> Rle_bool x y = false.
Proof.
intros x y Hxy.
case Rle_bool_spec ; intros H.
elim (Rlt_irrefl x).
now apply Rle_lt_trans with y.
apply refl_equal.
Qed.

End Rle_bool.

Section Rlt_bool.

Definition Rlt_bool x y :=
match Rcompare x y with
| Lt => true
| _ => false
end.

Inductive Rlt_bool_prop (x y : R) : bool -> Prop :=
| Rlt_bool_true_ : (x < y)%R -> Rlt_bool_prop x y true
| Rlt_bool_false_ : (y <= x)%R -> Rlt_bool_prop x y false.

Theorem Rlt_bool_spec :
forall x y, Rlt_bool_prop x y (Rlt_bool x y).
Proof.
intros x y.
unfold Rlt_bool.
case Rcompare_spec ; constructor.
exact H.
rewrite H.
apply Rle_refl.
now apply Rlt_le.
Qed.

Theorem negb_Rlt_bool :
forall x y,
negb (Rle_bool x y) = Rlt_bool y x.
Proof.
intros x y.
unfold Rlt_bool, Rle_bool.
rewrite Rcompare_sym.
now case Rcompare.
Qed.

Theorem negb_Rle_bool :
forall x y,
negb (Rlt_bool x y) = Rle_bool y x.
Proof.
intros x y.
unfold Rlt_bool, Rle_bool.
rewrite Rcompare_sym.
now case Rcompare.
Qed.

Theorem Rlt_bool_true :
forall x y,
(x < y)%R -> Rlt_bool x y = true.
Proof.
intros x y Hxy.
rewrite <- negb_Rlt_bool.
now rewrite Rle_bool_false.
Qed.

Theorem Rlt_bool_false :
forall x y,
(y <= x)%R -> Rlt_bool x y = false.
Proof.
intros x y Hxy.
rewrite <- negb_Rlt_bool.
now rewrite Rle_bool_true.
Qed.

End Rlt_bool.

Section Req_bool.

Definition Req_bool x y :=
match Rcompare x y with
| Eq => true
| _ => false
end.

Inductive Req_bool_prop (x y : R) : bool -> Prop :=
| Req_bool_true_ : (x = y)%R -> Req_bool_prop x y true
| Req_bool_false_ : (x <> y)%R -> Req_bool_prop x y false.

Theorem Req_bool_spec :
forall x y, Req_bool_prop x y (Req_bool x y).
Proof.
intros x y.
unfold Req_bool.
case Rcompare_spec ; constructor.
now apply Rlt_not_eq.
easy.
now apply Rgt_not_eq.
Qed.

Theorem Req_bool_true :
forall x y,
(x = y)%R -> Req_bool x y = true.
Proof.
intros x y Hxy.
case Req_bool_spec ; intros H.
apply refl_equal.
exact Hxy.
Qed.

Theorem Req_bool_false :
forall x y,
(x <> y)%R -> Req_bool x y = false.
Proof.
intros x y Hxy.
case Req_bool_spec ; intros H.
exact H.
apply refl_equal.
Qed.

End Req_bool.

Section Floor_Ceil.

Zfloor and Zceil
Definition Zfloor (x : R) := (up x - 1)%Z.

Theorem Zfloor_lb :
forall x : R,
(Z2R (Zfloor x) <= x)%R.
Proof.
intros x.
unfold Zfloor.
rewrite Z2R_minus.
simpl.
rewrite Z2R_IZR.
apply Rplus_le_reg_r with (1 - x)%R.
ring_simplify.
exact (proj2 (archimed x)).
Qed.

Theorem Zfloor_ub :
forall x : R,
(x < Z2R (Zfloor x) + 1)%R.
Proof.
intros x.
unfold Zfloor.
rewrite Z2R_minus.
unfold Rminus.
rewrite Rplus_assoc.
rewrite Rplus_opp_l, Rplus_0_r.
rewrite Z2R_IZR.
exact (proj1 (archimed x)).
Qed.

Theorem Zfloor_lub :
forall n x,
(Z2R n <= x)%R ->
(n <= Zfloor x)%Z.
Proof.
intros n x Hnx.
apply Zlt_succ_le.
apply lt_Z2R.
apply Rle_lt_trans with (1 := Hnx).
unfold Zsucc.
rewrite Z2R_plus.
apply Zfloor_ub.
Qed.

Theorem Zfloor_imp :
forall n x,
(Z2R n <= x < Z2R (n + 1))%R ->
Zfloor x = n.
Proof.
intros n x Hnx.
apply Zle_antisym.
apply Zlt_succ_le.
apply lt_Z2R.
apply Rle_lt_trans with (2 := proj2 Hnx).
apply Zfloor_lb.
now apply Zfloor_lub.
Qed.

Theorem Zfloor_Z2R :
forall n,
Zfloor (Z2R n) = n.
Proof.
intros n.
apply Zfloor_imp.
split.
apply Rle_refl.
apply Z2R_lt.
apply Zlt_succ.
Qed.

Theorem Zfloor_le :
forall x y, (x <= y)%R ->
(Zfloor x <= Zfloor y)%Z.
Proof.
intros x y Hxy.
apply Zfloor_lub.
apply Rle_trans with (2 := Hxy).
apply Zfloor_lb.
Qed.

Definition Zceil (x : R) := (- Zfloor (- x))%Z.

Theorem Zceil_ub :
forall x : R,
(x <= Z2R (Zceil x))%R.
Proof.
intros x.
unfold Zceil.
rewrite Z2R_opp.
apply Ropp_le_cancel.
rewrite Ropp_involutive.
apply Zfloor_lb.
Qed.

Theorem Zceil_glb :
forall n x,
(x <= Z2R n)%R ->
(Zceil x <= n)%Z.
Proof.
intros n x Hnx.
unfold Zceil.
apply Zopp_le_cancel.
rewrite Zopp_involutive.
apply Zfloor_lub.
rewrite Z2R_opp.
now apply Ropp_le_contravar.
Qed.

Theorem Zceil_imp :
forall n x,
(Z2R (n - 1) < x <= Z2R n)%R ->
Zceil x = n.
Proof.
intros n x Hnx.
unfold Zceil.
rewrite <- (Zopp_involutive n).
apply f_equal.
apply Zfloor_imp.
split.
rewrite Z2R_opp.
now apply Ropp_le_contravar.
rewrite <- (Zopp_involutive 1).
rewrite <- Zopp_plus_distr.
rewrite Z2R_opp.
now apply Ropp_lt_contravar.
Qed.

Theorem Zceil_Z2R :
forall n,
Zceil (Z2R n) = n.
Proof.
intros n.
unfold Zceil.
rewrite <- Z2R_opp, Zfloor_Z2R.
apply Zopp_involutive.
Qed.

Theorem Zceil_le :
forall x y, (x <= y)%R ->
(Zceil x <= Zceil y)%Z.
Proof.
intros x y Hxy.
apply Zceil_glb.
apply Rle_trans with (1 := Hxy).
apply Zceil_ub.
Qed.

Theorem Zceil_floor_neq :
forall x : R,
(Z2R (Zfloor x) <> x)%R ->
(Zceil x = Zfloor x + 1)%Z.
Proof.
intros x Hx.
apply Zceil_imp.
split.
ring_simplify (Zfloor x + 1 - 1)%Z.
apply Rnot_le_lt.
intros H.
apply Hx.
apply Rle_antisym.
apply Zfloor_lb.
exact H.
apply Rlt_le.
rewrite Z2R_plus.
apply Zfloor_ub.
Qed.

Definition Ztrunc x := if Rlt_bool x 0 then Zceil x else Zfloor x.

Theorem Ztrunc_Z2R :
forall n,
Ztrunc (Z2R n) = n.
Proof.
intros n.
unfold Ztrunc.
case Rlt_bool_spec ; intro H.
apply Zceil_Z2R.
apply Zfloor_Z2R.
Qed.

Theorem Ztrunc_floor :
forall x,
(0 <= x)%R ->
Ztrunc x = Zfloor x.
Proof.
intros x Hx.
unfold Ztrunc.
case Rlt_bool_spec ; intro H.
elim Rlt_irrefl with x.
now apply Rlt_le_trans with R0.
apply refl_equal.
Qed.

Theorem Ztrunc_ceil :
forall x,
(x <= 0)%R ->
Ztrunc x = Zceil x.
Proof.
intros x Hx.
unfold Ztrunc.
case Rlt_bool_spec ; intro H.
apply refl_equal.
rewrite (Rle_antisym _ _ Hx H).
change 0%R with (Z2R 0).
rewrite Zceil_Z2R.
apply Zfloor_Z2R.
Qed.

Theorem Ztrunc_le :
forall x y, (x <= y)%R ->
(Ztrunc x <= Ztrunc y)%Z.
Proof.
intros x y Hxy.
unfold Ztrunc at 1.
case Rlt_bool_spec ; intro Hx.
unfold Ztrunc.
case Rlt_bool_spec ; intro Hy.
now apply Zceil_le.
apply Zle_trans with 0%Z.
apply Zceil_glb.
now apply Rlt_le.
now apply Zfloor_lub.
rewrite Ztrunc_floor.
now apply Zfloor_le.
now apply Rle_trans with x.
Qed.

Theorem Ztrunc_opp :
forall x,
Ztrunc (- x) = Zopp (Ztrunc x).
Proof.
intros x.
unfold Ztrunc at 2.
case Rlt_bool_spec ; intros Hx.
rewrite Ztrunc_floor.
apply sym_eq.
apply Zopp_involutive.
rewrite <- Ropp_0.
apply Ropp_le_contravar.
now apply Rlt_le.
rewrite Ztrunc_ceil.
unfold Zceil.
now rewrite Ropp_involutive.
rewrite <- Ropp_0.
now apply Ropp_le_contravar.
Qed.

Theorem Ztrunc_abs :
forall x,
Ztrunc (Rabs x) = Zabs (Ztrunc x).
Proof.
intros x.
rewrite Ztrunc_floor. 2: apply Rabs_pos.
unfold Ztrunc.
case Rlt_bool_spec ; intro H.
rewrite Rabs_left with (1 := H).
rewrite Zabs_non_eq.
apply sym_eq.
apply Zopp_involutive.
apply Zceil_glb.
now apply Rlt_le.
rewrite Rabs_pos_eq with (1 := H).
apply sym_eq.
apply Zabs_eq.
now apply Zfloor_lub.
Qed.

Theorem Ztrunc_lub :
forall n x,
(Z2R n <= Rabs x)%R ->
(n <= Zabs (Ztrunc x))%Z.
Proof.
intros n x H.
rewrite <- Ztrunc_abs.
rewrite Ztrunc_floor. 2: apply Rabs_pos.
now apply Zfloor_lub.
Qed.

Definition Zaway x := if Rlt_bool x 0 then Zfloor x else Zceil x.

Theorem Zaway_Z2R :
forall n,
Zaway (Z2R n) = n.
Proof.
intros n.
unfold Zaway.
case Rlt_bool_spec ; intro H.
apply Zfloor_Z2R.
apply Zceil_Z2R.
Qed.

Theorem Zaway_ceil :
forall x,
(0 <= x)%R ->
Zaway x = Zceil x.
Proof.
intros x Hx.
unfold Zaway.
case Rlt_bool_spec ; intro H.
elim Rlt_irrefl with x.
now apply Rlt_le_trans with R0.
apply refl_equal.
Qed.

Theorem Zaway_floor :
forall x,
(x <= 0)%R ->
Zaway x = Zfloor x.
Proof.
intros x Hx.
unfold Zaway.
case Rlt_bool_spec ; intro H.
apply refl_equal.
rewrite (Rle_antisym _ _ Hx H).
change 0%R with (Z2R 0).
rewrite Zfloor_Z2R.
apply Zceil_Z2R.
Qed.

Theorem Zaway_le :
forall x y, (x <= y)%R ->
(Zaway x <= Zaway y)%Z.
Proof.
intros x y Hxy.
unfold Zaway at 1.
case Rlt_bool_spec ; intro Hx.
unfold Zaway.
case Rlt_bool_spec ; intro Hy.
now apply Zfloor_le.
apply le_Z2R.
apply Rle_trans with 0%R.
apply Rlt_le.
apply Rle_lt_trans with (2 := Hx).
apply Zfloor_lb.
apply Rle_trans with (1 := Hy).
apply Zceil_ub.
rewrite Zaway_ceil.
now apply Zceil_le.
now apply Rle_trans with x.
Qed.

Theorem Zaway_opp :
forall x,
Zaway (- x) = Zopp (Zaway x).
Proof.
intros x.
unfold Zaway at 2.
case Rlt_bool_spec ; intro H.
rewrite Zaway_ceil.
unfold Zceil.
now rewrite Ropp_involutive.
apply Rlt_le.
now apply Ropp_0_gt_lt_contravar.
rewrite Zaway_floor.
apply sym_eq.
apply Zopp_involutive.
rewrite <- Ropp_0.
now apply Ropp_le_contravar.
Qed.

Theorem Zaway_abs :
forall x,
Zaway (Rabs x) = Zabs (Zaway x).
Proof.
intros x.
rewrite Zaway_ceil. 2: apply Rabs_pos.
unfold Zaway.
case Rlt_bool_spec ; intro H.
rewrite Rabs_left with (1 := H).
rewrite Zabs_non_eq.
apply (f_equal (fun v => - Zfloor v)%Z).
apply Ropp_involutive.
apply le_Z2R.
apply Rlt_le.
apply Rle_lt_trans with (2 := H).
apply Zfloor_lb.
rewrite Rabs_pos_eq with (1 := H).
apply sym_eq.
apply Zabs_eq.
apply le_Z2R.
apply Rle_trans with (1 := H).
apply Zceil_ub.
Qed.

End Floor_Ceil.

Section Zdiv_Rdiv.

Theorem Zfloor_div :
forall x y,
y <> Z0 ->
Zfloor (Z2R x / Z2R y) = (x / y)%Z.
Proof.
intros x y Zy.
generalize (Z_div_mod_eq_full x y Zy).
intros Hx.
rewrite Hx at 1.
assert (Zy': Z2R y <> R0).
now apply eq_Z2R.
unfold Rdiv.
rewrite Z2R_plus, Rmult_plus_distr_r, Z2R_mult.
replace (Z2R y * Z2R (x / y) * / Z2R y)%R with (Z2R (x / y)) by now field.
apply Zfloor_imp.
rewrite Z2R_plus.
assert (0 <= Z2R (x mod y) * / Z2R y < 1)%R.
*)assert (forall x' y', (0 < y')%Z -> 0 <= Z2R (x' mod y') * / Z2R y' < 1)%R.
. *)clear.
intros x y Hy.
split.
apply Rmult_le_pos.
apply (Z2R_le 0).
refine (proj1 (Z_mod_lt _ _ _)).
now apply Zlt_gt.
apply Rlt_le.
apply Rinv_0_lt_compat.
now apply (Z2R_lt 0).
apply Rmult_lt_reg_r with (Z2R y).
now apply (Z2R_lt 0).
rewrite Rmult_1_l, Rmult_assoc, Rinv_l, Rmult_1_r.
apply Z2R_lt.
eapply Z_mod_lt.
now apply Zlt_gt.
apply Rgt_not_eq.
now apply (Z2R_lt 0).
. *)destruct (Z_lt_le_dec y 0) as [Hy|Hy].
rewrite <- Rmult_opp_opp.
rewrite Ropp_inv_permute with (1 := Zy').
rewrite <- 2!Z2R_opp.
rewrite <- Zmod_opp_opp.
apply H.
clear -Hy. omega.
apply H.
clear -Zy Hy. omega.
*)split.
pattern (Z2R (x / y)) at 1 ; rewrite <- Rplus_0_r.
apply Rplus_le_compat_l.
apply H.
apply Rplus_lt_compat_l.
apply H.
Qed.

End Zdiv_Rdiv.

Section pow.

Theorem radix_pos : (0 < Z2R r)%R.
Proof.
destruct r as (v, Hr). simpl.
apply (Z2R_lt 0).
apply Zlt_le_trans with 2%Z.
easy.
now apply Zle_bool_imp_le.
Qed.

Well-used function called bpow for computing the power function β^e
Definition bpow e :=
match e with
| Zpos p => Z2R (Zpower_pos r p)
| Zneg p => Rinv (Z2R (Zpower_pos r p))
| Z0 => 1%R
end.

Theorem Z2R_Zpower_pos :
forall n m,
Z2R (Zpower_pos n m) = powerRZ (Z2R n) (Zpos m).
Proof.
intros.
rewrite Zpower_pos_nat.
simpl.
induction (nat_of_P m).
apply refl_equal.
unfold Zpower_nat.
simpl.
rewrite Z2R_mult.
apply Rmult_eq_compat_l.
exact IHn0.
Qed.

Theorem bpow_powerRZ :
forall e,
bpow e = powerRZ (Z2R r) e.
Proof.
destruct e ; unfold bpow.
reflexivity.
now rewrite Z2R_Zpower_pos.
now rewrite Z2R_Zpower_pos.
Qed.

Theorem bpow_ge_0 :
forall e : Z, (0 <= bpow e)%R.
Proof.
intros.
rewrite bpow_powerRZ.
apply powerRZ_le.
Qed.

Theorem bpow_gt_0 :
forall e : Z, (0 < bpow e)%R.
Proof.
intros.
rewrite bpow_powerRZ.
apply powerRZ_lt.
Qed.

Theorem bpow_plus :
forall e1 e2 : Z, (bpow (e1 + e2) = bpow e1 * bpow e2)%R.
Proof.
intros.
repeat rewrite bpow_powerRZ.
apply Rgt_not_eq.
Qed.

Theorem bpow_1 :
bpow 1 = Z2R r.
Proof.
unfold bpow, Zpower_pos. simpl.
now rewrite Zmult_1_r.
Qed.

Theorem bpow_plus1 :
forall e : Z, (bpow (e + 1) = Z2R r * bpow e)%R.
Proof.
intros.
rewrite <- bpow_1.
rewrite <- bpow_plus.
now rewrite Zplus_comm.
Qed.

Theorem bpow_opp :
forall e : Z, (bpow (-e) = /bpow e)%R.
Proof.
intros [|p|p].
apply eq_sym, Rinv_1.
now change (-Zpos p)%Z with (Zneg p).
change (-Zneg p)%Z with (Zpos p).
simpl; rewrite Rinv_involutive; trivial.
apply Rgt_not_eq.
apply (bpow_gt_0 (Zpos p)).
Qed.

Theorem Z2R_Zpower_nat :
forall e : nat,
Z2R (Zpower_nat r e) = bpow (Z_of_nat e).
Proof.
intros [|e].
split.
rewrite <- nat_of_P_o_P_of_succ_nat_eq_succ.
rewrite <- Zpower_pos_nat.
now rewrite <- Zpos_eq_Z_of_nat_o_nat_of_P.
Qed.

Theorem Z2R_Zpower :
forall e : Z,
(0 <= e)%Z ->
Z2R (Zpower r e) = bpow e.
Proof.
intros [|e|e] H.
split.
split.
now elim H.
Qed.

Theorem bpow_lt :
forall e1 e2 : Z,
(e1 < e2)%Z -> (bpow e1 < bpow e2)%R.
Proof.
intros e1 e2 H.
replace e2 with (e1 + (e2 - e1))%Z by ring.
rewrite <- (Rmult_1_r (bpow e1)).
rewrite bpow_plus.
apply Rmult_lt_compat_l.
apply bpow_gt_0.
assert (0 < e2 - e1)%Z by omega.
destruct (e2 - e1)%Z ; try discriminate H0.
clear.
rewrite <- Z2R_Zpower by easy.
apply (Z2R_lt 1).
now apply Zpower_gt_1.
Qed.

Theorem lt_bpow :
forall e1 e2 : Z,
(bpow e1 < bpow e2)%R -> (e1 < e2)%Z.
Proof.
intros e1 e2 H.
apply Zgt_lt.
apply Znot_le_gt.
intros H'.
apply Rlt_not_le with (1 := H).
destruct (Zle_lt_or_eq _ _ H').
apply Rlt_le.
now apply bpow_lt.
rewrite H0.
apply Rle_refl.
Qed.

Theorem bpow_le :
forall e1 e2 : Z,
(e1 <= e2)%Z -> (bpow e1 <= bpow e2)%R.
Proof.
intros e1 e2 H.
apply Rnot_lt_le.
intros H'.
apply Zle_not_gt with (1 := H).
apply Zlt_gt.
now apply lt_bpow.
Qed.

Theorem le_bpow :
forall e1 e2 : Z,
(bpow e1 <= bpow e2)%R -> (e1 <= e2)%Z.
Proof.
intros e1 e2 H.
apply Znot_gt_le.
intros H'.
apply Rle_not_lt with (1 := H).
apply bpow_lt.
now apply Zgt_lt.
Qed.

Theorem bpow_inj :
forall e1 e2 : Z,
bpow e1 = bpow e2 -> e1 = e2.
Proof.
intros.
apply Zle_antisym.
apply le_bpow.
now apply Req_le.
apply le_bpow.
now apply Req_le.
Qed.

Theorem bpow_exp :
forall e : Z,
bpow e = exp (Z2R e * ln (Z2R r)).
Proof.
positive case *)assert (forall e, bpow (Zpos e) = exp (Z2R (Zpos e) * ln (Z2R r))).
intros e.
unfold bpow.
rewrite Zpower_pos_nat.
unfold Z2R at 2.
rewrite P2R_INR.
induction (nat_of_P e).
rewrite Rmult_0_l.
now rewrite exp_0.
rewrite Zpower_nat_S.
rewrite S_INR.
rewrite Rmult_plus_distr_r.
rewrite exp_plus.
rewrite Rmult_1_l.
rewrite exp_ln.
rewrite <- IHn.
rewrite <- Z2R_mult.
now rewrite Zmult_comm.
general case *)intros [|e|e].
rewrite Rmult_0_l.
now rewrite exp_0.
apply H.
unfold bpow.
change (Z2R (Zpower_pos r e)) with (bpow (Zpos e)).
rewrite H.
rewrite <- exp_Ropp.
rewrite <- Ropp_mult_distr_l_reverse.
now rewrite <- Z2R_opp.
Qed.

Another well-used function for having the logarithm of a real number x to the base β
Record ln_beta_prop x := {
ln_beta_val :> Z ;
_ : (x <> 0)%R -> (bpow (ln_beta_val - 1)%Z <= Rabs x < bpow ln_beta_val)%R
}.

Definition ln_beta :
forall x : R, ln_beta_prop x.
Proof.
intros x.
set (fact := ln (Z2R r)).
. *)assert (0 < fact)%R.
apply exp_lt_inv.
rewrite exp_0.
unfold fact.
rewrite exp_ln.
apply (Z2R_lt 1).
. *)exists (Zfloor (ln (Rabs x) / fact) + 1)%Z.
intros Hx'.
generalize (Rabs_pos_lt _ Hx'). clear Hx'.
generalize (Rabs x). clear x.
intros x Hx.
rewrite 2!bpow_exp.
fold fact.
pattern x at 2 3 ; replace x with (exp (ln x * / fact * fact)).
split.
rewrite Z2R_minus.
apply exp_le.
apply Rmult_le_compat_r.
now apply Rlt_le.
unfold Rminus.
rewrite Z2R_plus.
rewrite Rplus_assoc.
rewrite Rplus_opp_r, Rplus_0_r.
apply Zfloor_lb.
apply exp_increasing.
apply Rmult_lt_compat_r.
exact H.
rewrite Z2R_plus.
apply Zfloor_ub.
rewrite Rmult_assoc.
rewrite Rinv_l.
rewrite Rmult_1_r.
now apply exp_ln.
now apply Rgt_not_eq.
Qed.

Theorem bpow_lt_bpow :
forall e1 e2,
(bpow (e1 - 1) < bpow e2)%R ->
(e1 <= e2)%Z.
Proof.
intros e1 e2 He.
rewrite (Zsucc_pred e1).
apply Zlt_le_succ.
now apply lt_bpow.
Qed.

Theorem bpow_unique :
forall x e1 e2,
(bpow (e1 - 1) <= x < bpow e1)%R ->
(bpow (e2 - 1) <= x < bpow e2)%R ->
e1 = e2.
Proof.
intros x e1 e2 (H1a,H1b) (H2a,H2b).
apply Zle_antisym ;
apply bpow_lt_bpow ;
apply Rle_lt_trans with x ;
assumption.
Qed.

Theorem ln_beta_unique :
forall (x : R) (e : Z),
(bpow (e - 1) <= Rabs x < bpow e)%R ->
ln_beta x = e :> Z.
Proof.
intros x e1 He.
destruct (Req_dec x 0) as [Hx|Hx].
elim Rle_not_lt with (1 := proj1 He).
rewrite Hx, Rabs_R0.
apply bpow_gt_0.
destruct (ln_beta x) as (e2, Hx2).
simpl.
apply bpow_unique with (2 := He).
now apply Hx2.
Qed.

Theorem ln_beta_opp :
forall x,
ln_beta (-x) = ln_beta x :> Z.
Proof.
intros x.
destruct (Req_dec x 0) as [Hx|Hx].
now rewrite Hx, Ropp_0.
destruct (ln_beta x) as (e, He).
simpl.
specialize (He Hx).
apply ln_beta_unique.
now rewrite Rabs_Ropp.
Qed.

Theorem ln_beta_abs :
forall x,
ln_beta (Rabs x) = ln_beta x :> Z.
Proof.
intros x.
unfold Rabs.
case Rcase_abs ; intros _.
apply ln_beta_opp.
apply refl_equal.
Qed.

Theorem ln_beta_unique_pos :
forall (x : R) (e : Z),
(bpow (e - 1) <= x < bpow e)%R ->
ln_beta x = e :> Z.
Proof.
intros x e1 He1.
rewrite <- ln_beta_abs.
apply ln_beta_unique.
rewrite 2!Rabs_pos_eq.
exact He1.
apply Rle_trans with (2 := proj1 He1).
apply bpow_ge_0.
apply Rabs_pos.
Qed.

Theorem ln_beta_le_abs :
forall x y,
(x <> 0)%R -> (Rabs x <= Rabs y)%R ->
(ln_beta x <= ln_beta y)%Z.
Proof.
intros x y H0x Hxy.
destruct (ln_beta x) as (ex, Hx).
destruct (ln_beta y) as (ey, Hy).
simpl.
apply bpow_lt_bpow.
specialize (Hx H0x).
apply Rle_lt_trans with (1 := proj1 Hx).
apply Rle_lt_trans with (1 := Hxy).
apply Hy.
intros Hy'.
apply Rlt_not_le with (1 := Rabs_pos_lt _ H0x).
apply Rle_trans with (1 := Hxy).
rewrite Hy', Rabs_R0.
apply Rle_refl.
Qed.

Theorem ln_beta_le :
forall x y,
(0 < x)%R -> (x <= y)%R ->
(ln_beta x <= ln_beta y)%Z.
Proof.
intros x y H0x Hxy.
apply ln_beta_le_abs.
now apply Rgt_not_eq.
rewrite 2!Rabs_pos_eq.
exact Hxy.
apply Rle_trans with (2 := Hxy).
now apply Rlt_le.
now apply Rlt_le.
Qed.

Lemma ln_beta_lt_pos :
forall x y,
(0 < x)%R -> (0 < y)%R ->
(ln_beta x < ln_beta y)%Z -> (x < y)%R.
Proof.
intros x y Px Py.
destruct (ln_beta x) as (ex, Hex).
destruct (ln_beta y) as (ey, Hey).
simpl.
intro H.
destruct Hex as (_,Hex); [now apply Rgt_not_eq|].
destruct Hey as (Hey,_); [now apply Rgt_not_eq|].
rewrite Rabs_right in Hex; [|now apply Rle_ge; apply Rlt_le].
rewrite Rabs_right in Hey; [|now apply Rle_ge; apply Rlt_le].
apply (Rlt_le_trans _ _ _ Hex).
apply Rle_trans with (bpow (ey - 1)); [|exact Hey].
now apply bpow_le; omega.
Qed.

Theorem ln_beta_bpow :
forall e, (ln_beta (bpow e) = e + 1 :> Z)%Z.
Proof.
intros e.
apply ln_beta_unique.
rewrite Rabs_right.
replace (e + 1 - 1)%Z with e by ring.
split.
apply Rle_refl.
apply bpow_lt.
apply Zlt_succ.
apply Rle_ge.
apply bpow_ge_0.
Qed.

Theorem ln_beta_mult_bpow :
forall x e, x <> 0%R ->
(ln_beta (x * bpow e) = ln_beta x + e :>Z)%Z.
Proof.
intros x e Zx.
destruct (ln_beta x) as (ex, Ex) ; simpl.
specialize (Ex Zx).
apply ln_beta_unique.
rewrite Rabs_mult.
rewrite (Rabs_pos_eq (bpow e)) by apply bpow_ge_0.
split.
replace (ex + e - 1)%Z with (ex - 1 + e)%Z by ring.
rewrite bpow_plus.
apply Rmult_le_compat_r.
apply bpow_ge_0.
apply Ex.
rewrite bpow_plus.
apply Rmult_lt_compat_r.
apply bpow_gt_0.
apply Ex.
Qed.

Theorem ln_beta_le_bpow :
forall x e,
x <> 0%R ->
(Rabs x < bpow e)%R ->
(ln_beta x <= e)%Z.
Proof.
intros x e Zx Hx.
destruct (ln_beta x) as (ex, Ex) ; simpl.
specialize (Ex Zx).
apply bpow_lt_bpow.
now apply Rle_lt_trans with (Rabs x).
Qed.

Theorem ln_beta_gt_bpow :
forall x e,
(bpow e <= Rabs x)%R ->
(e < ln_beta x)%Z.
Proof.
intros x e Hx.
destruct (ln_beta x) as (ex, Ex) ; simpl.
apply lt_bpow.
apply Rle_lt_trans with (1 := Hx).
apply Ex.
intros Zx.
apply Rle_not_lt with (1 := Hx).
rewrite Zx, Rabs_R0.
apply bpow_gt_0.
Qed.

Theorem ln_beta_ge_bpow :
forall x e,
(bpow (e - 1) <= Rabs x)%R ->
(e <= ln_beta x)%Z.
Proof.
intros x e H.
destruct (Rlt_or_le (Rabs x) (bpow e)) as [Hxe|Hxe].
- (* Rabs x w bpow e *)
assert (ln_beta x = e :> Z) as Hln.
now apply ln_beta_unique; split.
rewrite Hln.
now apply Z.le_refl.
- (* bpow e <= Rabs x *)
apply Zlt_le_weak.
now apply ln_beta_gt_bpow.
Qed.

Theorem bpow_ln_beta_gt :
forall x,
(Rabs x < bpow (ln_beta x))%R.
Proof.
intros x.
destruct (Req_dec x 0) as [Zx|Zx].
rewrite Zx, Rabs_R0.
apply bpow_gt_0.
destruct (ln_beta x) as (ex, Ex) ; simpl.
now apply Ex.
Qed.

Theorem bpow_ln_beta_le :
forall x, (x <> 0)%R ->
(bpow (ln_beta x-1) <= Rabs x)%R.
Proof.
intros x Hx.
destruct (ln_beta x) as (ex, Ex) ; simpl.
now apply Ex.
Qed.

Theorem ln_beta_le_Zpower :
forall m e,
m <> Z0 ->
(Zabs m < Zpower r e)%Z->
(ln_beta (Z2R m) <= e)%Z.
Proof.
intros m e Zm Hm.
apply ln_beta_le_bpow.
exact (Z2R_neq m 0 Zm).
destruct (Zle_or_lt 0 e).
rewrite <- Z2R_abs, <- Z2R_Zpower with (1 := H).
now apply Z2R_lt.
elim Zm.
cut (Zabs m < 0)%Z.
now case m.
clear -Hm H.
now destruct e.
Qed.

Theorem ln_beta_gt_Zpower :
forall m e,
m <> Z0 ->
(Zpower r e <= Zabs m)%Z ->
(e < ln_beta (Z2R m))%Z.
Proof.
intros m e Zm Hm.
apply ln_beta_gt_bpow.
rewrite <- Z2R_abs.
destruct (Zle_or_lt 0 e).
rewrite <- Z2R_Zpower with (1 := H).
now apply Z2R_le.
apply Rle_trans with (bpow 0).
apply bpow_le.
now apply Zlt_le_weak.
apply (Z2R_le 1).
clear -Zm.
zify ; omega.
Qed.

Lemma ln_beta_mult :
forall x y,
(x <> 0)%R -> (y <> 0)%R ->
(ln_beta x + ln_beta y - 1 <= ln_beta (x * y) <= ln_beta x + ln_beta y)%Z.
Proof.
intros x y Hx Hy.
destruct (ln_beta x) as (ex, Hx2).
destruct (ln_beta y) as (ey, Hy2).
simpl.
destruct (Hx2 Hx) as (Hx21,Hx22); clear Hx2.
destruct (Hy2 Hy) as (Hy21,Hy22); clear Hy2.
assert (Hxy : (bpow (ex + ey - 1 - 1) <= Rabs (x * y))%R).
{ replace (ex + ey -1 -1)%Z with (ex - 1 + (ey - 1))%Z; [|ring].
rewrite bpow_plus.
rewrite Rabs_mult.
now apply Rmult_le_compat; try apply bpow_ge_0. }
assert (Hxy2 : (Rabs (x * y) < bpow (ex + ey))%R).
{ rewrite Rabs_mult.
rewrite bpow_plus.
apply Rmult_le_0_lt_compat; try assumption.
now apply Rle_trans with (bpow (ex - 1)); try apply bpow_ge_0.
now apply Rle_trans with (bpow (ey - 1)); try apply bpow_ge_0. }
split.
- now apply ln_beta_ge_bpow.
- apply ln_beta_le_bpow.
+ now apply Rmult_integral_contrapositive_currified.
+ assumption.
Qed.

Lemma ln_beta_plus :
forall x y,
(0 < y)%R -> (y <= x)%R ->
(ln_beta x <= ln_beta (x + y) <= ln_beta x + 1)%Z.
Proof.
assert (Hr : (2 <= r)%Z).
{ destruct r as (beta_val,beta_prop).
now apply Zle_bool_imp_le. }
intros x y Hy Hxy.
assert (Hx : (0 < x)%R) by apply (Rlt_le_trans _ _ _ Hy Hxy).
destruct (ln_beta x) as (ex,Hex); simpl.
destruct Hex as (Hex0,Hex1); [now apply Rgt_not_eq|].
assert (Haxy : (Rabs (x + y) < bpow (ex + 1))%R).
{ rewrite bpow_plus1.
apply Rlt_le_trans with (2 * bpow ex)%R.
- rewrite Rabs_pos_eq.
apply Rle_lt_trans with (2 * Rabs x)%R.
+ rewrite Rabs_pos_eq.
replace (2 * x)%R with (x + x)%R by ring.
now apply Rplus_le_compat_l.
now apply Rlt_le.
+ apply Rmult_lt_compat_l with (2 := Hex1).
exact Rlt_0_2.
+ rewrite <- (Rplus_0_l 0).
now apply Rlt_le, Rplus_lt_compat.
- apply Rmult_le_compat_r.
now apply bpow_ge_0.
now apply (Z2R_le 2). }
assert (Haxy2 : (bpow (ex - 1) <= Rabs (x + y))%R).
{ apply (Rle_trans _ _ _ Hex0).
rewrite Rabs_right; [|now apply Rgt_ge].
apply Rabs_ge; right.
rewrite <- (Rplus_0_r x) at 1.
apply Rplus_le_compat_l.
now apply Rlt_le. }
split.
- now apply ln_beta_ge_bpow.
- apply ln_beta_le_bpow.
+ now apply tech_Rplus; [apply Rlt_le|].
+ exact Haxy.
Qed.

Lemma ln_beta_minus :
forall x y,
(0 < y)%R -> (y < x)%R ->
(ln_beta (x - y) <= ln_beta x)%Z.
Proof.
intros x y Py Hxy.
assert (Px : (0 < x)%R) by apply (Rlt_trans _ _ _ Py Hxy).
apply ln_beta_le.
- now apply Rlt_Rminus.
- rewrite <- (Rplus_0_r x) at 2.
apply Rplus_le_compat_l.
rewrite <- Ropp_0.
now apply Ropp_le_contravar; apply Rlt_le.
Qed.

Lemma ln_beta_minus_lb :
forall x y,
(0 < x)%R -> (0 < y)%R ->
(ln_beta y <= ln_beta x - 2)%Z ->
(ln_beta x - 1 <= ln_beta (x - y))%Z.
Proof.
assert (Hbeta : (2 <= r)%Z).
{ destruct r as (beta_val,beta_prop).
now apply Zle_bool_imp_le. }
intros x y Px Py Hln.
assert (Oxy : (y < x)%R); [now apply ln_beta_lt_pos; [| |omega]|].
destruct (ln_beta x) as (ex,Hex).
destruct (ln_beta y) as (ey,Hey).
simpl in Hln |- *.
destruct Hex as (Hex,_); [now apply Rgt_not_eq|].
destruct Hey as (_,Hey); [now apply Rgt_not_eq|].
assert (Hbx : (bpow (ex - 2) + bpow (ex - 2) <= x)%R).
{ ring_simplify.
apply Rle_trans with (bpow (ex - 1)).
- replace (ex - 1)%Z with (ex - 2 + 1)%Z by ring.
rewrite bpow_plus1.
apply Rmult_le_compat_r; [now apply bpow_ge_0|].
now change 2%R with (Z2R 2); apply Z2R_le.
- now rewrite Rabs_right in Hex; [|apply Rle_ge; apply Rlt_le]. }
assert (Hby : (y < bpow (ex - 2))%R).
{ apply Rlt_le_trans with (bpow ey).
now rewrite Rabs_right in Hey; [|apply Rle_ge; apply Rlt_le].
now apply bpow_le. }
assert (Hbxy : (bpow (ex - 2) <= x - y)%R).
{ apply Ropp_lt_contravar in Hby.
apply Rlt_le in Hby.
replace (bpow (ex - 2))%R with (bpow (ex - 2) + bpow (ex - 2)
- bpow (ex - 2))%R by ring.
now apply Rplus_le_compat. }
apply ln_beta_ge_bpow.
replace (ex - 1 - 1)%Z with (ex - 2)%Z by ring.
now apply Rabs_ge; right.
Qed.

Lemma ln_beta_div :
forall x y : R,
(0 < x)%R -> (0 < y)%R ->
(ln_beta x - ln_beta y <= ln_beta (x / y) <= ln_beta x - ln_beta y + 1)%Z.
Proof.
intros x y Px Py.
destruct (ln_beta x) as (ex,Hex).
destruct (ln_beta y) as (ey,Hey).
simpl.
unfold Rdiv.
rewrite Rabs_right in Hex; [|now apply Rle_ge; apply Rlt_le].
rewrite Rabs_right in Hey; [|now apply Rle_ge; apply Rlt_le].
assert (Heiy : (bpow (- ey) < / y <= bpow (- ey + 1))%R).
{ split.
- rewrite bpow_opp.
apply Rinv_lt_contravar.
+ apply Rmult_lt_0_compat; [exact Py|].
now apply bpow_gt_0.
+ apply Hey.
now apply Rgt_not_eq.
- replace (_ + _)%Z with (- (ey - 1))%Z by ring.
rewrite bpow_opp.
apply Rinv_le; [now apply bpow_gt_0|].
apply Hey.
now apply Rgt_not_eq. }
split.
- apply ln_beta_ge_bpow.
apply Rabs_ge; right.
replace (_ - _)%Z with (ex - 1 - ey)%Z by ring.
unfold Zminus at 1; rewrite bpow_plus.
apply Rmult_le_compat.
+ now apply bpow_ge_0.
+ now apply bpow_ge_0.
+ apply Hex.
now apply Rgt_not_eq.
+ apply Rlt_le; apply Heiy.
- assert (Pxy : (0 < x * / y)%R).
{ apply Rmult_lt_0_compat; [exact Px|].
now apply Rinv_0_lt_compat. }
apply ln_beta_le_bpow.
+ now apply Rgt_not_eq.
+ rewrite Rabs_right; [|now apply Rle_ge; apply Rlt_le].
replace (_ + 1)%Z with (ex + (- ey + 1))%Z by ring.
rewrite bpow_plus.
apply Rlt_le_trans with (bpow ex * / y)%R.
* apply Rmult_lt_compat_r; [now apply Rinv_0_lt_compat|].
apply Hex.
now apply Rgt_not_eq.
* apply Rmult_le_compat_l; [now apply bpow_ge_0|].
apply Heiy.
Qed.

Lemma ln_beta_sqrt :
forall x,
(0 < x)%R ->
(2 * ln_beta (sqrt x) - 1 <= ln_beta x <= 2 * ln_beta (sqrt x))%Z.
Proof.
intros x Px.
assert (H : (bpow (2 * ln_beta (sqrt x) - 1 - 1) <= Rabs x
< bpow (2 * ln_beta (sqrt x)))%R).
{ split.
- apply Rge_le; rewrite <- (sqrt_def x) at 1;
[|now apply Rlt_le]; apply Rle_ge.
rewrite Rabs_mult.
replace (_ - _)%Z with (ln_beta (sqrt x) - 1
+ (ln_beta (sqrt x) - 1))%Z by ring.
rewrite bpow_plus.
assert (H : (bpow (ln_beta (sqrt x) - 1) <= Rabs (sqrt x))%R).
{ destruct (ln_beta (sqrt x)) as (esx,Hesx); simpl.
apply Hesx.
apply Rgt_not_eq; apply Rlt_gt.
now apply sqrt_lt_R0. }
now apply Rmult_le_compat; [now apply bpow_ge_0|now apply bpow_ge_0| |].
- rewrite <- (sqrt_def x) at 1; [|now apply Rlt_le].
rewrite Rabs_mult.
change 2%Z with (1 + 1)%Z; rewrite Zmult_plus_distr_l;
rewrite Zmult_1_l.
rewrite bpow_plus.
assert (H : (Rabs (sqrt x) < bpow (ln_beta (sqrt x)))%R).
{ destruct (ln_beta (sqrt x)) as (esx,Hesx); simpl.
apply Hesx.
apply Rgt_not_eq; apply Rlt_gt.
now apply sqrt_lt_R0. }
now apply Rmult_lt_compat; [now apply Rabs_pos|now apply Rabs_pos| |]. }
split.
- now apply ln_beta_ge_bpow.
- now apply ln_beta_le_bpow; [now apply Rgt_not_eq|].
Qed.

End pow.

Section Bool.

Theorem eqb_sym :
forall x y, Bool.eqb x y = Bool.eqb y x.
Proof.
now intros [|] [|].
Qed.

Theorem eqb_false :
forall x y, x = negb y -> Bool.eqb x y = false.
Proof.
now intros [|] [|].
Qed.

Theorem eqb_true :
forall x y, x = y -> Bool.eqb x y = true.
Proof.
now intros [|] [|].
Qed.

End Bool.

Section cond_Ropp.

Definition cond_Ropp (b : bool) m := if b then Ropp m else m.

Theorem Z2R_cond_Zopp :
forall b m,
Z2R (cond_Zopp b m) = cond_Ropp b (Z2R m).
Proof.
intros [|] m.
apply Z2R_opp.
apply refl_equal.
Qed.

Theorem abs_cond_Ropp :
forall b m,
Rabs (cond_Ropp b m) = Rabs m.
Proof.
intros [|] m.
apply Rabs_Ropp.
apply refl_equal.
Qed.

Theorem cond_Ropp_Rlt_bool :
forall m,
cond_Ropp (Rlt_bool m 0) m = Rabs m.
Proof.
intros m.
apply sym_eq.
case Rlt_bool_spec ; intros Hm.
now apply Rabs_left.
now apply Rabs_pos_eq.
Qed.

Theorem cond_Ropp_involutive :
forall b x,
cond_Ropp b (cond_Ropp b x) = x.
Proof.
intros [|] x.
apply Ropp_involutive.
apply refl_equal.
Qed.

Theorem cond_Ropp_even_function :
forall {A : Type} (f : R -> A),
(forall x, f (Ropp x) = f x) ->
forall b x, f (cond_Ropp b x) = f x.
Proof.
now intros A f Hf [|] x ; simpl.
Qed.

Theorem cond_Ropp_odd_function :
forall (f : R -> R),
(forall x, f (Ropp x) = Ropp (f x)) ->
forall b x, f (cond_Ropp b x) = cond_Ropp b (f x).
Proof.
now intros f Hf [|] x ; simpl.
Qed.

Theorem cond_Ropp_inj :
forall b x y,
cond_Ropp b x = cond_Ropp b y -> x = y.
Proof.
intros b x y H.
rewrite <- (cond_Ropp_involutive b x), H.
apply cond_Ropp_involutive.
Qed.

Theorem cond_Ropp_mult_l :
forall b x y,
cond_Ropp b (x * y) = (cond_Ropp b x * y)%R.
Proof.
intros [|] x y.
apply sym_eq.
apply Ropp_mult_distr_l_reverse.
apply refl_equal.
Qed.

Theorem cond_Ropp_mult_r :
forall b x y,
cond_Ropp b (x * y) = (x * cond_Ropp b y)%R.
Proof.
intros [|] x y.
apply sym_eq.
apply Ropp_mult_distr_r_reverse.
apply refl_equal.
Qed.

Theorem cond_Ropp_plus :
forall b x y,
cond_Ropp b (x + y) = (cond_Ropp b x + cond_Ropp b y)%R.
Proof.
intros [|] x y.
apply Ropp_plus_distr.
apply refl_equal.
Qed.

End cond_Ropp.

LPO taken from Coquelicot

Theorem LPO_min :
forall P : nat -> Prop, (forall n, P n \/ ~ P n) ->
{n : nat | P n /\ forall i, (i < n)%nat -> ~ P i} + {forall n, ~ P n}.
Proof.
assert (Hi: forall n, (0 < INR n + 1)%R).
intros N.
rewrite <- S_INR.
apply lt_0_INR.
apply lt_0_Sn.
intros P HP.
set (E y := exists n, (P n /\ y = / (INR n + 1))%R \/ (~ P n /\ y = 0)%R).
assert (HE: forall n, P n -> E (/ (INR n + 1))%R).
intros n Pn.
exists n.
left.
now split.
assert (BE: is_upper_bound E 1).
intros x [y [[_ ->]|[_ ->]]].
rewrite <- Rinv_1 at 2.
apply Rinv_le.
exact Rlt_0_1.
rewrite <- S_INR.
apply (le_INR 1), le_n_S, le_0_n.
exact Rle_0_1.
destruct (completeness E) as [l [ub lub]].
now exists 1%R.
destruct (HP O) as [H0|H0].
exists 1%R.
exists O.
left.
apply (conj H0).
rewrite Rplus_0_l.
apply sym_eq, Rinv_1.
exists 0%R.
exists O.
right.
now split.
destruct (Rle_lt_dec l 0) as [Hl|Hl].
right.
intros n Pn.
apply Rle_not_lt with (1 := Hl).
apply Rlt_le_trans with (/ (INR n + 1))%R.
now apply Rinv_0_lt_compat.
apply ub.
now apply HE.
left.
set (N := Zabs_nat (up (/l) - 2)).
exists N.
assert (HN: (INR N + 1 = IZR (up (/ l)) - 1)%R).
unfold N.
rewrite INR_IZR_INZ.
rewrite inj_Zabs_nat.
replace (IZR (up (/ l)) - 1)%R with (IZR (up (/ l) - 2) + 1)%R.
apply (f_equal (fun v => IZR v + 1)%R).
apply Zabs_eq.
apply Zle_minus_le_0.
apply (Zlt_le_succ 1).
apply lt_IZR.
apply Rle_lt_trans with (/l)%R.
apply Rmult_le_reg_r with (1 := Hl).
rewrite Rmult_1_l, Rinv_l by now apply Rgt_not_eq.
apply lub.
exact BE.
apply archimed.
rewrite minus_IZR.
simpl.
ring.
assert (H: forall i, (i < N)%nat -> ~ P i).
intros i HiN Pi.
unfold is_upper_bound in ub.
refine (Rle_not_lt _ _ (ub (/ (INR i + 1))%R _) _).
now apply HE.
rewrite <- (Rinv_involutive l) by now apply Rgt_not_eq.
apply Rinv_1_lt_contravar.
rewrite <- S_INR.
apply (le_INR 1).
apply le_n_S.
apply le_0_n.
apply Rlt_le_trans with (INR N + 1)%R.
apply Rplus_lt_compat_r.
now apply lt_INR.
rewrite HN.
apply Rplus_le_reg_r with (-/l + 1)%R.
ring_simplify.
apply archimed.
destruct (HP N) as [PN|PN].
now split.
elimtype False.
refine (Rle_not_lt _ _ (lub (/ (INR (S N) + 1))%R _) _).
intros x [y [[Py ->]|[_ ->]]].
destruct (eq_nat_dec y N) as [HyN|HyN].
elim PN.
now rewrite <- HyN.
apply Rinv_le.
apply Hi.
apply Rplus_le_compat_r.
apply Rnot_lt_le.
intros Hy.
refine (H _ _ Py).
apply INR_lt in Hy.
clear -Hy HyN.
omega.
now apply Rlt_le, Rinv_0_lt_compat.
rewrite S_INR, HN.
ring_simplify (IZR (up (/ l)) - 1 + 1)%R.
rewrite <- (Rinv_involutive l) at 2 by now apply Rgt_not_eq.
apply Rinv_1_lt_contravar.
rewrite <- Rinv_1.
apply Rinv_le.
exact Hl.
now apply lub.
apply archimed.
Qed.

Theorem LPO :
forall P : nat -> Prop, (forall n, P n \/ ~ P n) ->
{n : nat | P n} + {forall n, ~ P n}.
Proof.
intros P HP.
destruct (LPO_min P HP) as [[n [Pn _]]|Pn].
left.
now exists n.
now right.
Qed.

Lemma LPO_Z : forall P : Z -> Prop, (forall n, P n \/ ~P n) ->
{n : Z| P n} + {forall n, ~ P n}.
Proof.
intros P H.
destruct (LPO (fun n => P (Z.of_nat n))) as [J|J].
intros n; apply H.
destruct J as (n, Hn).
left; now exists (Z.of_nat n).
destruct (LPO (fun n => P (-Z.of_nat n)%Z)) as [K|K].
intros n; apply H.
destruct K as (n, Hn).
left; now exists (-Z.of_nat n)%Z.
right; intros n; case (Zle_or_lt 0 n); intros M.
rewrite <- (Zabs_eq n); trivial.
rewrite <- Zabs2Nat.id_abs.
apply J.
rewrite <- (Zopp_involutive n).
rewrite <- (Z.abs_neq n).
rewrite <- Zabs2Nat.id_abs.
apply K.
omega.
Qed.

A little tactic to simplify terms of the form bpow a * bpow b.
Ltac bpow_simplify :=
repeat
match goal with
| |- context [(bpow _ _ * bpow _ _)] =>
rewrite <- bpow_plus
| |- context [(?X1 * bpow _ _ * bpow _ _)] =>
rewrite (Rmult_assoc X1); rewrite <- bpow_plus
| |- context [(?X1 * (?X2 * bpow _ _) * bpow _ _)] =>
rewrite <- (Rmult_assoc X1 X2); rewrite (Rmult_assoc (X1 * X2));
rewrite <- bpow_plus
end;
repeat
match goal with
| |- context [(bpow _ ?X)] =>
progress ring_simplify X
end;
change (bpow _ 0) with 1;
repeat
match goal with
| |- context [(_ * 1)] =>
rewrite Rmult_1_r
end.