Module mathcomp.analysis.normedtype_theory.normed_module

From HB Require Import structures.
From mathcomp Require Import all_ssreflect ssralg ssrint ssrnum finmap matrix.
From mathcomp Require Import rat interval zmodp vector fieldext falgebra.
From mathcomp Require Import archimedean.
From mathcomp Require Import mathcomp_extra unstable boolp classical_sets.
From mathcomp Require Import functions cardinality set_interval.
From mathcomp Require Import interval_inference ereal reals topology.
From mathcomp Require Import function_spaces real_interval.
From mathcomp Require Import prodnormedzmodule tvs num_normedtype.
From mathcomp Require Import ereal_normedtype pseudometric_normed_Zmodule.

# Normed modules We define normed modules. We prove the intermediate value theorem (IVT). ## Normed modules ``` normedModType K == interface type for a normed module structure over the numDomainType K The HB class is NormedModule. `|x| == the norm of x (notation from ssrnum.v) ``` We endow `numFieldType` with the types of norm-related notions (accessible with `Import numFieldNormedType.Exports`). ## Hulls ``` Rhull A == the real interval hull of a set A ``` ## Lipschitz functions ``` self_sub f x := f x.1 - f x.2 lipschitz_on f F == f is lipschitz near F k.-lipschitz_on f F == f is k.-lipschitz near F k.-lipschitz_A f == f is k.-lipschitz on A [lipschitz f x | x in A] == f is lipschitz on A [locally [lipschitz f x | x in A] == f is locally lipschitz on A [locally k.-lipschitz_A f] == f is locally k.-lipschitz on A contraction q f == f is q.-lipschitz and q < 1 is_contraction f == exists q, f is q.-lipschitz and q < 1 ```

Reserved Notation "k .-lipschitz_on f"
  (at level 2, format "k .-lipschitz_on f").
Reserved Notation "k .-lipschitz_ A f"
  (at level 2, A at level 0, format "k .-lipschitz_ A f").
Reserved Notation "k .-lipschitz f" (at level 2, format "k .-lipschitz f").
Reserved Notation "[ 'lipschitz' E | x 'in' A ]"
  (at level 0, x name, format "[ 'lipschitz' E | x 'in' A ]").

Set Implicit Arguments.
Unset Strict Implicit.
Unset Printing Implicit Defensive.

Import Order.TTheory GRing.Theory Num.Def Num.Theory.
Import numFieldTopology.Exports.

Local Open Scope classical_set_scope.
Local Open Scope ring_scope.

Modules with a norm depending on a numDomain

HB.mixin Record PseudoMetricNormedZmod_Tvs_isNormedModule K V
    of PseudoMetricNormedZmod K V & Tvs K V := {
  normrZ : forall (l : K) (x : V), `| l *: x | = `| l | * `| x |;
}.

#[short(type="normedModType")]
HB.structure Definition NormedModule (K : numDomainType) :=
  {T of PseudoMetricNormedZmod K T & Tvs K T
   & PseudoMetricNormedZmod_Tvs_isNormedModule K T}.

HB.factory Record PseudoMetricNormedZmod_Lmodule_isNormedModule (K : numFieldType) V
    of PseudoMetricNormedZmod K V & GRing.Lmodule K V := {
normrZ : forall (l : K) (x : V), `| l *: x | = `| l | * `| x |;
}.

HB.builders Context K V of PseudoMetricNormedZmod_Lmodule_isNormedModule K V.

Lemma add_continuous : continuous (fun x : V * V => x.1 + x.2).

Proof.

exact: add_continuous. Qed.

Lemma scale_continuous : continuous (fun z : K^o * V => z.1 *: z.2).

Proof.

move=> [/= k x]; apply/cvgrPdist_lt => _/posnumP[e]; near +oo_K => M.
near=> l z => /=; have M0 : 0 < M by [].
rewrite (@distm_lt_split _ _ (k *: z)) // -?(scalerBr, scalerBl) normrZ.
  rewrite (@le_lt_trans _ _ (M * `|x - z|)) ?ler_wpM2r -?ltr_pdivlMl//.
  by near: z; apply: cvgr_dist_lt; rewrite // mulr_gt0 ?invr_gt0.
rewrite (@le_lt_trans _ _ (`|k - l| * M)) ?ler_wpM2l -?ltr_pdivlMr//.
  by near: z; near: M; apply: cvg_bounded (@cvg_refl _ _).
by near: l; apply: cvgr_dist_lt; rewrite // divr_gt0.
Unshelve. all: by end_near. Qed.

Lemma locally_convex :
exists2 B : set (set V), (forall b, b \in B -> convex b) & basis B.

Proof.

exists [set B | exists x r, B = ball x r].
  move=> b; rewrite inE /= => [[x]] [r] -> z y l.
  rewrite !inE -!ball_normE /= => zx yx l0; rewrite -subr_gt0 => l1.
  have -> : x = l *: x + (1 - l) *: x by rewrite addrC scalerBl subrK scale1r.
  rewrite [X in `|X|](_ : _ = l *: (x - z) + (1 - l) *: (x - y)); last first.
    by rewrite opprD addrACA -scalerBr -scalerBr.
  rewrite (@le_lt_trans _ _ (`|l| * `|x - z| + `|1 - l| * `|x - y|))//.
    by rewrite -!normrZ ler_normD.
  rewrite (@lt_le_trans _ _ (`|l| * r + `|1 - l| * r ))//.
    rewrite ltr_leD//.
      by rewrite -ltr_pdivlMl ?mulrA ?mulVf ?mul1r // ?normrE ?gt_eqF.
    by rewrite -ler_pdivlMl ?mulrA ?mulVf ?mul1r ?ltW // ?normrE ?gt_eqF.
  by rewrite !gtr0_norm// -mulrDl addrC subrK mul1r.
split.
  move=> B [x] [r] ->.
  rewrite openE/= -ball_normE/= /interior => y /= bxy; rewrite -nbhs_ballE.
  exists (r - `|x - y|) => /=; first by rewrite subr_gt0.
  move=> z; rewrite -ball_normE/= ltrBrDr.
  by apply: le_lt_trans; rewrite [in leRHS]addrC ler_distD.
move=> x B; rewrite -nbhs_ballE/= => -[r] r0 Bxr /=.
by exists (ball x r) => //; split; [exists x, r|exact: ballxx].
Qed.

HB.instance Definition _ :=
Uniform_isTvs.Build K V add_continuous scale_continuous locally_convex.

HB.instance Definition _ :=
PseudoMetricNormedZmod_Tvs_isNormedModule.Build K V normrZ.

HB.end.

see also `Section standard_topology_pseudoMetricNormedZmod` in `pseudometric_normed_Zmodule.v`

Proof.

by rewrite /GRing.scale/= mulr1. Qed.

Lemma limf_esup_dnbhsN {R : realType} (f : R -> \bar R) (a : R) :
limf_esup f a^' = limf_esup (fun x => f (- x)%R) (- a)%R^'.

Proof.

rewrite /limf_esup dnbhsN image_comp/=.
congr (ereal_inf [set _ | _ in _]); apply/funext => A /=.
rewrite image_comp/= -compA (_ : _ \o _ = idfun)// funeqE => x/=.
by rewrite opprK.
Qed.

Lemma cvg_patch {R : realType} (f : R -> R^o) (a b : R) (x : R) : (a < b)%R ->
  x \in `]a, b[ ->
  f @ (x : subspace `[a, b]) --> f x ->
  (f \_ `[a, b] x) @[x --> x] --> f x.

Proof.

move=> ab xab xf; apply/cvgrPdist_lt => /= e e0.
move/cvgrPdist_lt : xf => /(_ e e0) xf.
near=> z.
rewrite patchE ifT//; last first.
  rewrite inE; apply: subset_itv_oo_cc.
  by near: z; exact: near_in_itvoo.
near: z.
rewrite /prop_near1 /nbhs/= /nbhs_subspace ifT// in xf; last first.
  by rewrite inE/=; exact: subset_itv_oo_cc xab.
case: xf => x0 /= x00 xf.
near=> z.
apply: xf => //=.
rewrite inE; apply: subset_itv_oo_cc.
by near: z; exact: near_in_itvoo.
Unshelve. all: by end_near. Qed.

Section NormedModule_numDomainType.
Variables (K : numDomainType) (V : normedModType K).

Lemma normrZV (x : V) : `|x| \in GRing.unit -> `| `| x |^-1 *: x | = 1.

Proof.

by move=> nxu; rewrite normrZ normrV// normr_id mulVr. Qed.

Lemma near_shift (y x : V) (P : set V) :
(\near x, P x) = (\forall z \near y, (P \o shift (x - y)) z).

Proof.

(* rewrite propeqE nbhs0P [X in _ <-> X]nbhs0P/= -propeqE. *)
(* by apply: eq_near => e; rewrite ![_ + e]addrC addrACA subrr addr0. *)
rewrite propeqE; split=> /= /nbhs_normP [_/posnumP[e] ye];
apply/nbhs_normP; exists e%:num => //= t et.
by apply: ye; rewrite /= distrC addrCA [x + _]addrC addrK distrC.
by have /= := ye (t - (x - y)); rewrite opprB addrCA subrKA addrNK; exact.
Qed.

Lemma cvg_comp_shift {T : Type} (x y : V) (f : V -> T) :
(f \o shift x) @ y = f @ (y + x).

Proof.

rewrite funeqE => A; rewrite /= !near_simpl (near_shift (y + x)).
by rewrite (_ : _ \o _ = A \o f) // funeqE=> z; rewrite /= opprD addNKr addrNK.
Qed.

Lemma ball_open (x : V) (r : K) : 0 < r -> open (ball x r).

Proof.

rewrite openE -ball_normE /interior => r0 y /= Bxy; near=> z.
rewrite /= (le_lt_trans (ler_distD y _ _)) // addrC -ltrBrDr.
by near: z; apply: cvgr_dist_lt; rewrite // subr_gt0.
Unshelve. all: by end_near. Qed.

Lemma ball_open_nbhs (x : V) (r : K) : 0 < r -> open_nbhs x (ball x r).

Proof.

by move=> e0; split; [exact: ball_open|exact: ballxx]. Qed.

End NormedModule_numDomainType.

Definition self_sub (K : numDomainType) (V W : normedModType K)
(f : V -> W) (x : V * V) : W := f x.1 - f x.2.
Arguments self_sub {K V W} f x /.

Section NormedModule_numFieldType.
Variables (K : numFieldType) (V : normedModType K).

Lemma normfZV (x : V) : x != 0 -> `| `|x|^-1 *: x | = 1.

Proof.

by rewrite -normr_eq0 -unitfE => /normrZV->. Qed.

Lemma cvg_at_rightE (f : K -> V) x :
cvg (f @ x^') -> lim (f @ x^') = lim (f @ x^'+).

Proof.

move=> cvfx; apply/Logic.eq_sym.
apply: (@cvg_lim _ _ _ (at_right _)) => // A /cvfx /nbhs_ballP [_ /posnumP[e] xe_A].
by exists e%:num => //= y xe_y; rewrite lt_def => /andP [xney _]; apply: xe_A.
Qed.

Lemma cvg_at_leftE (f : K -> V) x :
cvg (f @ x^') -> lim (f @ x^') = lim (f @ x^'-).

Proof.

move=> cvfx; apply/Logic.eq_sym.
apply: (@cvg_lim _ _ _ (at_left _)) => // A /cvfx /nbhs_ballP [_ /posnumP[e] xe_A].
exists e%:num => //= y xe_y; rewrite lt_def => /andP [xney _].
by apply: xe_A => //; rewrite eq_sym.
Qed.

Lemma scale_continuous : continuous (fun z : K * V => z.1 *: z.2).

Proof.

exact: scale_continuous. Abort.

Arguments scale_continuous _ _ : clear implicits.

Lemma scaler_continuous k : continuous (fun x : V => k *: x).

Proof.

by move=> x; apply: (cvg_comp2 (cvg_cst _) cvg_id (scale_continuous _ _ (_, _))).
Qed.

Lemma scalel_continuous (x : V) : continuous (fun k : K => k *: x).

Proof.

by move=> k; apply: (cvg_comp2 cvg_id (cvg_cst _) (scale_continuous _ _ (_, _))).
Qed.

End NormedModule_numFieldType.
Arguments cvg_at_rightE {K V} f x.
Arguments cvg_at_leftE {K V} f x.

Section NormedModule_continuous.
Variables (K : numFieldType) (U V : normedModType K).

Lemma continuous_shift (f : U -> V) u :
{for u, continuous f} = {for 0, continuous (f \o shift u)}.

Proof.

by rewrite [in RHS]forE /continuous_at/= add0r cvg_comp_shift add0r.
Qed.

Lemma continuous_withinNshiftx (f : U -> V) u :
f \o shift u @ 0^' --> f u <-> {for u, continuous f}.

Proof.

rewrite continuous_shift; split=> [cfu|].
by apply/(continuous_withinNx _ _).2/(cvg_trans cfu); rewrite /= add0r.
by move/(continuous_withinNx _ _).1/cvg_trans; apply; rewrite /= add0r.
Qed.

End NormedModule_continuous.

Lemma near0Z {R : numFieldType} {V : normedModType R} (y : V) (P : set V) :
(\forall x \near 0, P x) -> (\forall k \near 0, P (k *: y)).

Proof.

by have /= := @scalel_continuous R V y 0 _; rewrite scale0r; apply.
Qed.

Section NVS_continuity_mul.
Context {K : numFieldType}.

Lemma mul_continuous : continuous (fun z : K * K => z.1 * z.2).

Proof.

exact: scale_continuous. Qed.

Lemma mulrl_continuous (x : K) : continuous ( *%R x).

Proof.

exact: scaler_continuous. Qed.

Lemma mulrr_continuous (y : K) : continuous ( *%R^~ y : K -> K).

Proof.

exact: scalel_continuous. Qed.

Lemma inv_continuous (x : K) : x != 0 -> {for x, continuous (@GRing.inv K)}.

Proof.

move=> x_neq0; have nx_gt0 : `|x| > 0 by rewrite normr_gt0.
apply/(@cvgrPdist_ltp _ _ _ (nbhs x)); near (0 : K)^'+ => d. near=> e.
near=> y; have y_neq0 : y != 0 by near: y; apply: (cvgr_neq0 x).
rewrite /= -div1r -[y^-1]div1r -mulNr addf_div// mul1r mulN1r normrM normfV.
rewrite ltr_pdivrMr ?normr_gt0 ?mulf_neq0// (@lt_le_trans _ _ (e * d))//.
by near: y; apply: cvgr_distC_lt => //; rewrite mulr_gt0.
rewrite ler_pM2l => //=; rewrite normrM -ler_pdivrMl//.
near: y; apply: (cvgr_norm_ge x) => //; rewrite ltr_pdivrMl//.
by near: d; apply: nbhs_right_lt; rewrite mulr_gt0.
Unshelve. all: by end_near. Qed.

End NVS_continuity_mul.

Section cvg_composition_normed.
Context {K : numFieldType} {V : normedModType K} {T : Type}.
Context (F : set_system T) {FF : Filter F}.
Implicit Types (f g : T -> V) (s : T -> K) (k : K) (x : T) (a b : V).

Lemma cvgZ s f k a : s @ F --> k -> f @ F --> a ->
s x *: f x @[x --> F] --> k *: a.

Proof.

move=> ? ?; apply: continuous2_cvg => //.
have := (@scale_continuous K V (k, a)).
rewrite /continuous_at/=.
exact.
Qed.

Lemma is_cvgZ s f : cvg (s @ F) ->
cvg (f @ F) -> cvg ((fun x => s x *: f x) @ F).

Proof.

by have := cvgP _ (cvgZ _ _); apply. Qed.

Lemma cvgZl s k a : s @ F --> k -> s x *: a @[x --> F] --> k *: a.

Proof.

by move=> ?; apply: cvgZ => //; exact: cvg_cst. Qed.

Lemma is_cvgZl s a : cvg (s @ F) -> cvg ((fun x => s x *: a) @ F).

Proof.

by have := cvgP _ (cvgZl _); apply. Qed.

Lemma cvgZr k f a : f @ F --> a -> k \*: f @ F --> k *: a.

Proof.

apply: cvgZ => //; exact: cvg_cst. Qed.

Lemma is_cvgZr k f : cvg (f @ F) -> cvg (k *: f @ F).

Proof.

by have := cvgP _ (cvgZr _); apply. Qed.

Lemma is_cvgZrE k f : k != 0 -> cvg (k *: f @ F) = cvg (f @ F).

Proof.

move=> k_neq0; rewrite propeqE; split => [/(@cvgZr k^-1)|/(@cvgZr k)/cvgP//].
by under [_ \*: _]funext => x /= do rewrite scalerK//; apply: cvgP.
Qed.

End cvg_composition_normed.

Section cvg_composition_field.
Context {K : numFieldType} {T : Type}.
Context (F : set_system T) {FF : Filter F}.
Implicit Types (f g : T -> K) (a b : K).

Lemma cvgV f a : a != 0 -> f @ F --> a -> f\^-1 @ F --> a^-1.

Proof.

by move=> k_neq0 f_cvg; apply: continuous_cvg => //; apply: inv_continuous.
Qed.

Lemma cvgVP f a : a != 0 -> f\^-1 @ F --> a^-1 <-> f @ F --> a.

Proof.

move=> aN0; split=> /(cvgV _); last exact.
by rewrite invrK invr_eq0 inv_funK; apply.
Qed.

Lemma is_cvgV f : lim (f @ F) != 0 -> cvg (f @ F) -> cvg (f\^-1 @ F).

Proof.

by move=> /cvgV cvf /cvf /cvgP. Qed.

Lemma cvgM f g a b : f @ F --> a -> g @ F --> b -> (f \* g) @ F --> a * b.

Proof.

exact: cvgZ. Qed.

Lemma cvgMl f a b : f @ F --> a -> (f x * b) @[x --> F] --> a * b.

Proof.

exact: cvgZl. Qed.

Lemma cvgMr g a b : g @ F --> b -> (a * g x) @[x --> F] --> a * b.

Proof.

exact: cvgZr. Qed.

Lemma is_cvgM f g : cvg (f @ F) -> cvg (g @ F) -> cvg (f \* g @ F).

Proof.

exact: is_cvgZ. Qed.

Lemma is_cvgMr g a (f := fun=> a) : cvg (g @ F) -> cvg (f \* g @ F).

Proof.

exact: is_cvgZr. Qed.

Lemma is_cvgMrE g a (f := fun=> a) : a != 0 -> cvg (f \* g @ F) = cvg (g @ F).

Proof.

exact: is_cvgZrE. Qed.

Lemma is_cvgMl f a (g := fun=> a) : cvg (f @ F) -> cvg (f \* g @ F).

Proof.

move=> f_cvg; have -> : f \* g = g \* f by apply/funeqP=> x; rewrite /= mulrC.
exact: is_cvgMr.
Qed.

Lemma is_cvgMlE f a (g := fun=> a) : a != 0 -> cvg (f \* g @ F) = cvg (f @ F).

Proof.

move=> a_neq0; have -> : f \* g = g \* f by apply/funeqP=> x; rewrite /= mulrC.
exact: is_cvgMrE.
Qed.

End cvg_composition_field.

Section limit_composition_normed.
Context {K : numFieldType} {V : normedModType K} {T : Type}.
Context (F : set_system T) {FF : ProperFilter F}.
Implicit Types (f g : T -> V) (s : T -> K) (k : K) (x : T) (a : V).

Lemma limZ s f : cvg (s @ F) -> cvg (f @ F) ->
lim ((fun x => s x *: f x) @ F) = lim (s @ F) *: lim (f @ F).

Proof.

by move=> ? ?; apply: cvg_lim => //; apply: cvgZ. Qed.

Lemma limZl s a : cvg (s @ F) ->
lim ((fun x => s x *: a) @ F) = lim (s @ F) *: a.

Proof.

by move=> ?; apply: cvg_lim => //; apply: cvgZl. Qed.

Lemma limZr k f : cvg (f @ F) -> lim (k *: f @ F) = k *: lim (f @ F).

Proof.

by move=> ?; apply: cvg_lim => //; apply: cvgZr. Qed.

End limit_composition_normed.

Section limit_composition_field.
Context {K : numFieldType} {T : Type}.
Context (F : set_system T) {FF : ProperFilter F}.
Implicit Types (f g : T -> K).

Lemma limM f g : cvg (f @ F) -> cvg (g @ F) ->
lim (f \* g @ F) = lim (f @ F) * lim (g @ F).

Proof.

by move=> ? ?; apply: cvg_lim => //; apply: cvgM. Qed.

End limit_composition_field.

Section cvg_composition_field_proper.
Context {K : numFieldType} {T : Type}.
Context (F : set_system T) {FF : ProperFilter F}.
Implicit Types (f g : T -> K) (a b : K).

Lemma limV f : lim (f @ F) != 0 -> lim (f\^-1 @ F) = (lim (f @ F))^-1.

Proof.

by move=> ?; apply: cvg_lim => //; apply: cvgV => //; apply: cvgNpoint.
Qed.

Lemma is_cvgVE f : lim (f @ F) != 0 -> cvg (f\^-1 @ F) = cvg (f @ F).

Proof.

move=> ?; apply/propeqP; split=> /is_cvgV; last exact.
by rewrite inv_funK; apply; rewrite limV ?invr_eq0//.
Qed.

End cvg_composition_field_proper.

Section ProperFilterRealType.
Context {T : Type} {F : set_system T} {FF : ProperFilter F} {R : realFieldType}.
Implicit Types (f g h : T -> R) (a b : R).

Lemma cvgr_to_ge f a b : f @ F --> a -> (\near F, b <= f F) -> b <= a.

Proof.

by move=> /[swap]/(closed_cvg _ (@closed_ge _ b))/[apply]. Qed.

Lemma cvgr_to_le f a b : f @ F --> a -> (\near F, f F <= b) -> a <= b.

Proof.

by move=> /[swap]/(closed_cvg _ (@closed_le _ b))/[apply]. Qed.

Lemma limr_ge x f : cvg (f @ F) -> (\near F, x <= f F) -> x <= lim (f @ F).

Proof.

exact: cvgr_to_ge. Qed.

Lemma limr_le x f : cvg (f @ F) -> (\near F, x >= f F) -> x >= lim (f @ F).

Proof.

exact: cvgr_to_le. Qed.

End ProperFilterRealType.

Section local_continuity.
Context {K : numFieldType} {V : normedModType K} {T : topologicalType}.
Implicit Types (f g : T -> V) (s t : T -> K) (x : T) (k : K) (a : V).

Lemma continuousN (f : T -> V) x :
{for x, continuous f} -> {for x, continuous (fun x => - f x)}.

Proof.

by move=> ?; apply: cvgN. Qed.

Lemma continuousD f g x :
{for x, continuous f} -> {for x, continuous g} ->
{for x, continuous (f + g)}.

Proof.

by move=> f_cont g_cont; apply: cvgD. Qed.

Lemma continuousB f g x :
{for x, continuous f} -> {for x, continuous g} ->
{for x, continuous (f - g)}.

Proof.

by move=> f_cont g_cont; apply: cvgB. Qed.

Lemma continuousZ s f x :
{for x, continuous s} -> {for x, continuous f} ->
{for x, continuous (fun x => s x *: f x)}.

Proof.

by move=> ? ?; apply: cvgZ. Qed.

Lemma continuousZr f k x :
{for x, continuous f} -> {for x, continuous (k \*: f)}.

Proof.

by move=> ?; apply: cvgZr. Qed.

Lemma continuousZl s a x :
{for x, continuous s} -> {for x, continuous (fun z => s z *: a)}.

Proof.

by move=> ?; apply: cvgZl. Qed.

Lemma continuousM s t x :
{for x, continuous s} -> {for x, continuous t} ->
{for x, continuous (s \* t)}.

Proof.

by move=> f_cont g_cont; apply: cvgM. Qed.

Lemma continuousV s x : s x != 0 ->
{for x, continuous s} -> {for x, continuous (fun x => (s x)^-1%R)}.

Proof.

by move=> ?; apply: cvgV. Qed.

End local_continuity.

Section cvg_fin.
Context {R : numFieldType}.

Section filter.
Context {F : set_system \bar R} {FF : Filter F}.

Lemma fine_fcvg a : F --> a%:E -> fine @ F --> a.

Proof.

move=> /(_ _)/= Fa; apply/cvgrPdist_lt=> // _/posnumP[e]; rewrite near_simpl.
by apply: Fa; apply/nbhs_EFin => /=; apply: (@cvgr_dist_lt _ _ _ (nbhs a)).
(* BUG: using cvgr_dist_lt without (nbhs _) expands the definition of nbhs, *)
(* so that it is not recognized as a filter anymore *)
Qed.

Lemma fcvg_is_fine a : F --> a%:E -> \near F, F \is a fin_num.

Proof.

by apply; apply/nbhs_EFin; near=> x. Unshelve. all: by end_near. Qed.

End filter.

Section limit.
Context {I : Type} {F : set_system I} {FF : Filter F} (f : I -> \bar R).

Lemma fine_cvg a : f @ F --> a%:E -> fine \o f @ F --> a.

Proof.

exact: fine_fcvg. Qed.

Lemma cvg_is_fine a : f @ F --> a%:E -> \near F, f F \is a fin_num.

Proof.

exact: fcvg_is_fine. Qed.

Lemma cvg_EFin a : (\near F, f F \is a fin_num) -> fine \o f @ F --> a ->
f @ F --> a%:E.

Proof.

move=> Ffin Fa P/= /nbhs_EFin /Fa; rewrite !near_simpl.
by apply: filterS2 Ffin => x /fineK->.
Qed.

Lemma fine_cvgP a :
f @ F --> a%:E <-> (\near F, f F \is a fin_num) /\ fine \o f @ F --> a.

Proof.

by split;[split;[exact: (@cvg_is_fine a)|exact: fine_cvg]|case; apply: cvg_EFin].
Qed.

Lemma neq0_fine_cvgP a : a != 0 -> f @ F --> a%:E <-> fine \o f @ F --> a.

Proof.

move=> a_neq0; split=> [|Fa]; first exact: fine_cvg.
apply: cvg_EFin=> //; near (0 : R)^'+ => e.
have lea : e <= `|a| by near: e; apply: nbhs_right_le; rewrite normr_gt0.
near=> x; have : `|a - fine (f x)| < e by near: x; apply: cvgr_dist_lt.
by case: f=> //=; rewrite subr0; apply: contra_ltT.
Unshelve. all: by end_near. Qed.

End limit.

End cvg_fin.

Section ecvg_realFieldType.
Context {I} {F : set_system I} {FF : Filter F} {R : realFieldType}.
Implicit Types f g u v : I -> \bar R.
Local Open Scope ereal_scope.

Lemma cvgeD f g a b :
a +? b -> f @ F --> a -> g @ F --> b -> f \+ g @ F --> a + b.

Proof.

have yE u v x : u @ F --> +oo -> v @ F --> x%:E -> u \+ v @ F --> +oo.
  move=> /cvgeyPge/= foo /fine_cvgP[Fg gb]; apply/cvgeyPgey.
  near=> A; near=> n; have /(_ _)/wrap[//|Fgn] := near Fg n.
  rewrite -leeBlDr// (@le_trans _ _ (A - (x - 1))%:E)//; last by near: n.
  rewrite ?EFinB leeB// leeBlDr// -[v n]fineK// -EFinD lee_fin.
  by rewrite ler_distlDr// ltW//; near: n; apply: cvgr_dist_lt.
have NyE u v x : u @ F --> -oo -> v @ F --> x%:E -> u \+ v @ F --> -oo.
  move=> /cvgeNyPle/= foo /fine_cvgP -[Fg gb]; apply/cvgeNyPleNy.
  near=> A; near=> n; have /(_ _)/wrap[//|Fgn] := near Fg n.
  rewrite -leeBrDr// (@le_trans _ _ (A - (x + 1))%:E)//; first by near: n.
  rewrite ?EFinB ?EFinD leeB// -[v n]fineK// -EFinD lee_fin.
  by rewrite ler_distlCDr// ltW//; near: n; apply: cvgr_dist_lt.
have yyE u v : u @ F --> +oo -> v @ F --> +oo -> u \+ v @ F --> +oo.
  move=> /cvgeyPge foo /cvgeyPge goo; apply/cvgeyPge => A; near=> y.
  by rewrite -[leLHS]adde0 leeD//; near: y; [apply: foo|apply: goo].
have NyNyE u v : u @ F --> -oo -> v @ F --> -oo -> u \+ v @ F --> -oo.
  move=> /cvgeNyPle foo /cvgeNyPle goo; apply/cvgeNyPle => A; near=> y.
  by rewrite -[leRHS]adde0 leeD//; near: y; [apply: foo|apply: goo].
have addfC u v : u \+ v = v \+ u.
  by apply/funeqP => x; rewrite /= addeC.
move: a b => [a| |] [b| |] //= _; rewrite ?(addey, addye, addeNy, addNye)//=;
  do ?by [apply: yE|apply: NyE|apply: yyE|apply: NyNyE].
- move=> /fine_cvgP[Ff fa] /fine_cvgP[Fg ga]; rewrite -EFinD.
  apply/fine_cvgP; split.
    by near do [rewrite fin_numD; apply/andP; split].
  apply: (@cvg_trans _ ((fine \o f) \+ (fine \o g) @ F))%R; last exact: cvgD.
  by apply: near_eq_cvg; near do rewrite /= fineD//.
- by move=> /[swap]; rewrite addfC; apply: yE.
- by move=> /[swap]; rewrite addfC; apply: NyE.
Unshelve. all: by end_near. Qed.

Lemma cvgeN f x : f @ F --> x -> - f x @[x --> F] --> - x.

Proof.

by move=> ?; apply: continuous_cvg => //; exact: oppe_continuous. Qed.

Lemma cvgeNP f a : - f x @[x --> F] --> - a <-> f @ F --> a.

Proof.

by split=> /cvgeN//; rewrite oppeK//; under eq_cvg do rewrite /= oppeK.
Qed.

Lemma cvgeB f g a b :
a +? - b -> f @ F --> a -> g @ F --> b -> f \- g @ F --> a - b.

Proof.

by move=> ab fa gb; apply: cvgeD => //; exact: cvgeN. Qed.

Lemma sube_cvg0 f (k : \bar R) :
k \is a fin_num -> (fun x => f x - k) @ F --> 0 <-> f @ F --> k.

Proof.

move=> kfin; split.
move=> /cvgeD-/(_ (cst k) _ isT (cvg_cst _)).
by rewrite add0e; under eq_fun => x do rewrite subeK//.
move: k kfin => [k _ fk| |]//; rewrite -(@subee _ k%:E)//.
by apply: cvgeB => //; exact: cvg_cst.
Qed.

Lemma abse_continuous : continuous (@abse R).

Proof.

case=> [r|A /= [r [rreal rA]]|A /= [r [rreal rA]]]/=.
- exact/(cvg_comp _ _ (@norm_continuous _ R r)).
- by exists r; split => // y ry; apply: rA; rewrite (lt_le_trans ry)// lee_abs.
- exists (- r)%R; rewrite realN; split => // y; rewrite EFinN -lteNr => yr.
by apply: rA; rewrite (lt_le_trans yr)// -abseN lee_abs.
Qed.

Lemma cvg_abse f (a : \bar R) : f @ F --> a -> `|f x|%E @[x --> F] --> `|a|%E.

Proof.

by apply: continuous_cvg => //; exact: abse_continuous. Qed.

Lemma is_cvg_abse (f : I -> \bar R) : cvg (f @ F) -> cvg (`|f x|%E @[x --> F]).

Proof.

by move/cvg_abse/cvgP. Qed.

Lemma is_cvgeN f : cvg (f @ F) -> cvg (\- f @ F).

Proof.

by move=> /cvg_ex[l fl]; apply: (cvgP (- l)); exact: cvgeN. Qed.

Lemma is_cvgeNE f : cvg (\- f @ F) = cvg (f @ F).

Proof.

rewrite propeqE; split=> /cvgeNP/cvgP//.
by under eq_is_cvg do rewrite oppeK.
Qed.

Lemma mule_continuous (r : R) : continuous (mule r%:E).

Proof.

rewrite /continuous_at; wlog r0 : r / (r > 0)%R => [hwlog|].
  have [r0|r0|->] := ltrgtP r 0; do ?exact: hwlog; last first.
    by move=> x; rewrite mul0e; apply: cvg_near_cst; near=> y; rewrite mul0e.
  have -> : *%E r%:E = \- ( *%E (- r)%:E ).
    by apply/funeqP=> x /=; rewrite EFinN mulNe oppeK.
  move=> x; apply: (continuous_comp (hwlog (- r)%R _ _)); rewrite ?oppr_gt0//.
  exact: oppe_continuous.
move=> [s||]/=.
- rewrite -EFinM; apply: cvg_EFin => /=.
    by apply/nbhs_EFin; near do rewrite fin_numM//.
  move=> P /= Prs; apply/nbhs_EFin=> //=.
  by apply: near_fun => //=; apply: continuousM => //=; apply: cvg_cst.
- rewrite gt0_muley ?lte_fin// => A [u [realu uA]].
  exists (r^-1 * u)%R; split; first by rewrite realM// realV realE ltW.
  by move=> x rux; apply: uA; move: rux; rewrite EFinM lte_pdivrMl.
- rewrite gt0_muleNy ?lte_fin// => A [u [realu uA]].
  exists (r^-1 * u)%R; split; first by rewrite realM// realV realE ltW.
  by move=> x xru; apply: uA; move: xru; rewrite EFinM lte_pdivlMl.
Unshelve. all: by end_near. Qed.

Lemma cvgeZl f x y : y \is a fin_num ->
f @ F --> x -> (fun n => y * f n) @ F --> y * x.

Proof.

by move: y => [r| |]// _ /cvg_comp; apply; exact: mule_continuous. Qed.

Lemma is_cvgeZl f y : y \is a fin_num ->
cvg (f @ F) -> cvg ((fun n => y * f n) @ F).

Proof.

by move=> fy /(cvgeZl fy)/cvgP. Qed.

Lemma cvgeZr f x y : y \is a fin_num ->
f @ F --> x -> (fun n => f n * y) @ F --> x * y.

Proof.

by move=> ? ?; rewrite muleC; under eq_fun do rewrite muleC; exact: cvgeZl.
Qed.

Lemma is_cvgeZr f y : y \is a fin_num ->
cvg (f @ F) -> cvg ((fun n => f n * y) @ F).

Proof.

by move=> fy /(cvgeZr fy)/cvgP. Qed.

Lemma cvg_abse0P f : abse \o f @ F --> 0 <-> f @ F --> 0.

Proof.

split; last by move=> /cvg_abse; rewrite abse0.
move=> /cvg_ballP f0; apply/cvg_ballP => _/posnumP[e].
have := [elaborate f0 _ (gt0 e)].
rewrite !near_simpl => absf0; rewrite near_simpl.
apply: filterS absf0 => x /=; rewrite /ball/= /ereal_ball !contract0 !sub0r !normrN.
have [fx0|fx0] := leP 0 (f x); first by rewrite gee0_abs.
by rewrite (lte0_abs fx0) contractN normrN.
Qed.

Let cvgeM_gt0_pinfty f g b :
(0 < b)%R -> f @ F --> +oo -> g @ F --> b%:E -> f \* g @ F --> +oo.

Proof.

move=> b_gt0 /cvgeyPge foo /fine_cvgP[gfin gb]; apply/cvgeyPgey.
near (0%R : R)^'+ => e; near=> A; near=> n.
rewrite (@le_trans _ _ (f n * e%:E))// ?lee_pmul// ?lee_fin//.
- by rewrite -lee_pdivrMr ?divr_gt0//; near: n; apply: foo.
- by rewrite (@le_trans _ _ 1) ?lee_fin//; near: n; apply: foo.
rewrite -(@fineK _ (g n)) ?lee_fin; last by near: n; exact: gfin.
by near: n; apply: (cvgr_ge b).
Unshelve. all: end_near. Qed.

Let cvgeM_lt0_pinfty f g b :
(b < 0)%R -> f @ F --> +oo -> g @ F --> b%:E -> f \* g @ F --> -oo.

Proof.

move=> b0 /cvgeyPge foo /fine_cvgP -[gfin gb]; apply/cvgeNyPleNy.
near (0%R : R)^'+ => e; near=> A; near=> n.
rewrite -leeN2 -muleN (@le_trans _ _ (f n * e%:E))//.
by rewrite -lee_pdivrMr ?mulr_gt0 ?oppr_gt0//; near: n; apply: foo.
rewrite lee_pmul ?lee_fin//.
by rewrite (@le_trans _ _ 1) ?lee_fin//; near: n; apply: foo.
rewrite -(@fineK _ (g n)) ?lee_fin; last by near: n; exact: gfin.
near: n; apply: (cvgr_ge (- b)); rewrite 1?cvgNP//.
by near: e; apply: nbhs_right_lt; rewrite oppr_gt0.
Unshelve. all: end_near. Qed.

Let cvgeM_gt0_ninfty f g b :
(0 < b)%R -> f @ F --> -oo -> g @ F --> b%:E -> f \* g @ F --> -oo.

Proof.

move=> b0 foo gb; under eq_fun do rewrite -muleNN.
apply: (@cvgeM_lt0_pinfty _ _ (- b)%R); first by rewrite oppr_lt0.
- by rewrite -(oppeK +oo); apply: cvgeN.
- by rewrite EFinN; apply: cvgeN.
Qed.

Let cvgeM_lt0_ninfty f g b :
(b < 0)%R -> f @ F --> -oo -> g @ F --> b%:E -> f \* g @ F --> +oo.

Proof.

move=> b0 foo gb; under eq_fun do rewrite -muleNN.
apply: (@cvgeM_gt0_pinfty _ _ (- b)%R); first by rewrite oppr_gt0.
- by rewrite -(oppeK +oo); apply: cvgeN.
- by rewrite EFinN; apply: cvgeN.
Qed.

Lemma cvgeM f g (a b : \bar R) :
a *? b -> f @ F --> a -> g @ F --> b -> f \* g @ F --> a * b.

Proof.

move=> [:apoo] [:bnoo] [:poopoo] [:poonoo]; move: a b => [a| |] [b| |] //.
- move=> _ /fine_cvgP[finf fa] /fine_cvgP[fing gb].
  apply/fine_cvgP; split.
    by near do apply: fin_numM; [apply: finf | apply: fing].
  apply: (@cvg_trans _ (((fine \o f) \* (fine \o g)) @ F)%R).
    apply: near_eq_cvg; near=> n => //=.
    rewrite -[in RHS](@fineK _ (f n)); last by near: n; exact: finf.
    by rewrite -[in RHS](@fineK _ (g n)) //; near: n; exact: fing.
  exact: cvgM.
- move: f g a; abstract: apoo.
  move=> {}f {}g {}a + fa goo; have [a0 _|a0 _|->] := ltgtP a 0%R.
  + rewrite mulry ltr0_sg// ?mulN1e.
    by under eq_fun do rewrite muleC; exact: (cvgeM_lt0_pinfty a0).
  + rewrite mulry gtr0_sg// ?mul1e.
    by under eq_fun do rewrite muleC; exact: (cvgeM_gt0_pinfty a0).
  + by rewrite /mule_def eqxx.
- move: f g a; abstract: bnoo.
  move=> {}f {}g {}a + fa goo; have [a0 _|a0 _|->] := ltgtP a 0%R.
  + rewrite mulrNy ltr0_sg// ?mulN1e.
    by under eq_fun do rewrite muleC; exact: (cvgeM_lt0_ninfty a0).
  + rewrite mulrNy gtr0_sg// ?mul1e.
    by under eq_fun do rewrite muleC; exact: (cvgeM_gt0_ninfty a0).
  + by rewrite /mule_def eqxx.
- rewrite mule_defC => ? foo gb; rewrite muleC.
  by under eq_fun do rewrite muleC; exact: apoo.
- move=> _; move: f g; abstract: poopoo.
  move=> {}f {}g /cvgeyPge foo /cvgeyPge goo.
  rewrite mulyy; apply/cvgeyPgey; near=> A; near=> n.
  have A_gt0 : (0 <= A)%R by [].
  by rewrite -[leLHS]mule1 lee_pmul//=; near: n; [apply: foo|apply: goo].
- move=> _; move: f g; abstract: poonoo.
  move=> {}f {}g /cvgeyPge foo /cvgeNyPle goo.
  rewrite mulyNy; apply/cvgeNyPle => A; near=> n.
  rewrite (@le_trans _ _ (g n))//; last by near: n; exact: goo.
  apply: lee_nemull; last by near: n; apply: foo.
  by rewrite (@le_trans _ _ (- 1)%:E)//; near: n; apply: goo; rewrite ltrN10.
- rewrite mule_defC => ? foo gb; rewrite muleC.
  by under eq_fun do rewrite muleC; exact: bnoo.
- move=> _ foo goo.
  by under eq_fun do rewrite muleC; exact: poonoo.
- move=> _ foo goo; rewrite mulNyNy -mulyy.
  by under eq_fun do rewrite -muleNN; apply: poopoo;
    rewrite -/(- -oo); apply: cvgeN.
Unshelve. all: end_near. Qed.

End ecvg_realFieldType.
#[deprecated(since="mathcomp-analysis 1.9.0", note="renamed to `sube_cvg0`")]
Notation cvge_sub0 := sube_cvg0 (only parsing).
#[deprecated(since="mathcomp-analysis 1.10.0", note="renamed to `cvgeZl`")]
Notation cvgeMl := cvgeZl (only parsing).
#[deprecated(since="mathcomp-analysis 1.10.0", note="renamed to `is_cvgeZl`")]
Notation is_cvgeMl := is_cvgeZl (only parsing).
#[deprecated(since="mathcomp-analysis 1.10.0", note="renamed to `cvgeZr`")]
Notation cvgeMr := cvgeZr (only parsing).
#[deprecated(since="mathcomp-analysis 1.10.0", note="renamed to `is_cvgeZr`")]
Notation is_cvgeMr := is_cvgeZr (only parsing).

Section max_cts.
Context {R : realType} {T : topologicalType}.

Lemma continuous_min (f g : T -> R^o) x :
{for x, continuous f} -> {for x, continuous g} ->
{for x, continuous (f \min g)}.

Proof.

move=> ctsf ctsg.
under [_ \min _]eq_fun => ? do rewrite minr_absE.
apply: cvgM; [|exact: cvg_cst]; apply: cvgD; first exact: cvgD.
by apply: cvgN; apply: cvg_norm; apply: cvgB.
Qed.

Lemma continuous_max (f g : T -> R^o) x :
{for x, continuous f} -> {for x, continuous g} ->
{for x, continuous (f \max g)}.

Proof.

move=> ctsf ctsg.
under [_ \max _]eq_fun => ? do rewrite maxr_absE.
apply: cvgM; [|exact: cvg_cst]; apply: cvgD; first exact: cvgD.
by apply: cvg_norm; apply: cvgB.
Qed.

End max_cts.

Lemma limit_pointP (T : archiFieldType) (A : set T) (x : T) :
limit_point A x <-> exists a_ : nat -> T,
[/\ a_ @` setT `<=` A, forall n, a_ n != x & a_ @ \oo --> x].

Proof.

split=> [Ax|[a_ [aTA a_x] ax]]; last first.
  move=> U /ax[m _ a_U]; near \oo => n; exists (a_ n); split => //.
  by apply aTA; exists n.
  by apply a_U; near: n; exists m.
pose U := fun n : nat => [set z : T | `|x - z| < n.+1%:R^-1].
suff /(_ _)/cid-/all_sig[a_ anx] : forall n, exists a, a != x /\ (U n `&` A) a.
  exists a_; split.
  - by move=> a [n _ <-]; have [? []] := anx n.
  - by move=> n; have [] := anx n.
  - apply/cvgrPdist_lt => _/posnumP[e]; near=> n; have [? [] Uan Aan] := anx n.
    by rewrite (lt_le_trans Uan)// ltW//; near: n; exact: near_infty_natSinv_lt.
move=> n; have : nbhs (x : T) (U n).
  by apply/(nbhs_ballP (x:T) (U n)); rewrite nbhs_ballE; exists n.+1%:R^-1 => //=.
by move/Ax/cid => [/= an [anx Aan Uan]]; exists an.
Unshelve. all: by end_near. Qed.

Lemma EFin_lim (R : realFieldType) (f : nat -> R) : cvgn f ->
limn (EFin \o f) = (limn f)%:E.

Proof.

move=> cf; apply: cvg_lim => //; move/cvg_ex : cf => [l fl].
by apply: (cvg_comp _ _ fl); rewrite (cvg_lim _ fl).
Qed.

Section ecvg_realFieldType_proper.
Context {I} {F : set_system I} {FF : ProperFilter F} {R : realFieldType}.
Implicit Types (f g : I -> \bar R) (u v : I -> R) (x : \bar R) (r : R).
Local Open Scope ereal_scope.

Lemma is_cvgeD f g :
lim (f @ F) +? lim (g @ F) -> cvg (f @ F) -> cvg (g @ F) -> cvg (f \+ g @ F).

Proof.

by move=> fg fc gc; have /(_ _)/cvgP := cvgeD fg fc gc. Qed.

Lemma limeD f g :
cvg (f @ F) -> cvg (g @ F) -> lim (f @ F) +? lim (g @ F) ->
lim (f \+ g @ F) = lim (f @ F) + lim (g @ F).

Proof.

by move=> cf cg fg; apply/cvg_lim => //; exact: cvgeD. Qed.

Lemma limeMl f y : y \is a fin_num -> cvg (f @ F) ->
lim ((fun n => y * f n) @ F) = y * lim (f @ F).

Proof.

by move=> yfn cf; apply/cvg_lim => //; exact: cvgeZl. Qed.

Lemma limeMr f y : y \is a fin_num -> cvg (f @ F) ->
lim ((fun n => f n * y) @ F) = lim (f @ F) * y.

Proof.

by move=> yfn cf; apply/cvg_lim => //; apply: cvgeZr. Qed.

Lemma is_cvgeM f g :
lim (f @ F) *? lim (g @ F) -> cvg (f @ F) -> cvg (g @ F) -> cvg (f \* g @ F).

Proof.

by move=> fg fc gc; have /(_ _)/cvgP := cvgeM fg fc gc. Qed.

Lemma limeM f g :
cvg (f @ F) -> cvg (g @ F) -> lim (f @ F) *? lim (g @ F) ->
lim (f \* g @ F) = lim (f @ F) * lim (g @ F).

Proof.

by move=> cf cg fg; apply/cvg_lim => //; exact: cvgeM. Qed.

Lemma limeN f : cvg (f @ F) -> lim (\- f @ F) = - lim (f @ F).

Proof.

by move=> cf; apply/cvg_lim => //; apply: cvgeN. Qed.

Lemma cvge_ge f a b : (\forall x \near F, b <= f x) -> f @ F --> a -> b <= a.

Proof.

by move=> ? fa; rewrite -(cvg_lim _ fa) ?lime_ge//=; apply: cvgP fa. Qed.

Lemma cvge_le f a b : (\forall x \near F, b >= f x) -> f @ F --> a -> b >= a.

Proof.

by move=> ? fa; rewrite -(cvg_lim _ fa) ?lime_le//=; apply: cvgP fa. Qed.

Lemma cvg_nnesum (J : Type) (r : seq J) (f : J -> I -> \bar R)
   (l : J -> \bar R) (P : pred J) :
  (forall j, P j -> \near F, 0 <= f j F) ->
  (forall j, P j -> f j @ F --> l j) ->
  \sum_(j <- r | P j) f j i @[i --> F] --> \sum_(j <- r | P j) l j.

Proof.

pose bigsimp := (big_nil, big_cons);
elim: r => [|x r IHr]/= f0 fl; rewrite bigsimp; under eq_fun do rewrite bigsimp.
exact: cvg_cst.
case: ifPn => [Px|Pnx]; last exact: IHr.
apply: cvgeD; [|exact: fl|exact: IHr].
by rewrite ge0_adde_def ?inE// ?sume_ge0// => [|j Pj];
rewrite (cvge_ge _ (fl _ _))//; apply: f0.
Qed.

Lemma lim_nnesum (J : Type) (r : seq J) (f : J -> I -> \bar R)
   (l : J -> \bar R) (P : pred J) :
  (forall j, P j -> \near F, 0 <= f j F) ->
  (forall j, P j -> cvg (f j @ F)) ->
  lim (\sum_(j <- r | P j) f j i @[i --> F]) = \sum_(j <- r | P j) (lim (f j @ F)).

Proof.

by move=> ? ?; apply/cvg_lim => //; apply: cvg_nnesum. Qed.

End ecvg_realFieldType_proper.

Section cvg_0_pinfty.
Context {R : realFieldType} {I : Type} {a : set_system I} {FF : Filter a}.
Implicit Types f : I -> R.

Lemma gtr0_cvgV0 f : (\near a, 0 < f a) -> f\^-1 @ a --> 0 <-> f @ a --> +oo.

Proof.

move=> f_gt0; split; last first.
  move=> /cvgryPgt cvg_f_oo; apply/cvgr0Pnorm_lt => _/posnumP[e].
  near=> i; rewrite gtr0_norm ?invr_gt0//=; last by near: i.
  by rewrite -ltf_pV2 ?qualifE/= ?invr_gt0 ?invrK//=; near: i.
move=> /cvgr0Pnorm_lt uB; apply/cvgryPgty.
near=> M; near=> i; suff: `|(f i)^-1| < M^-1.
  by rewrite gtr0_norm ?ltf_pV2 ?qualifE ?invr_gt0//=; near: i.
by near: i; apply: uB; rewrite ?invr_gt0.
Unshelve. all: by end_near. Qed.

Lemma cvgrVy f : (\near a, 0 < f a) -> f\^-1 @ a --> +oo <-> f @ a --> 0.

Proof.

by move=> f_gt0; rewrite -gtr0_cvgV0 ?inv_funK//; near do rewrite invr_gt0.
Unshelve. all: by end_near. Qed.

Lemma ltr0_cvgV0 f : (\near a, 0 > f a) -> f\^-1 @ a --> 0 <-> f @ a --> -oo.

Proof.

move=> fL0; rewrite -cvgNP oppr0 (_ : - f\^-1 = (- f)\^-1); last first.
by apply/funeqP => i; rewrite opprfctE/= invrN.
by rewrite gtr0_cvgV0 ?cvgNry//; near do rewrite oppr_gt0.
Unshelve. all: by end_near. Qed.

Lemma cvgrVNy f : (\near a, 0 > f a) -> f\^-1 @ a --> -oo <-> f @ a --> 0.

Proof.

by move=> f_lt0; rewrite -ltr0_cvgV0 ?inv_funK//; near do rewrite invr_lt0.
Unshelve. all: by end_near. Qed.

End cvg_0_pinfty.

Section FilterRealType.
Context {T : Type} {a : set_system T} {Fa : Filter a} {R : realFieldType}.
Implicit Types f g h : T -> R.

Lemma squeeze_cvgr f h g : (\near a, f a <= g a <= h a) ->
forall (l : R), f @ a --> l -> h @ a --> l -> g @ a --> l.

Proof.

move=> fgh l lfa lga; apply/cvgrPdist_lt => e e_gt0.
near=> x; have /(_ _)/andP[//|fg gh] := near fgh x.
rewrite distrC ltr_distl (lt_le_trans _ fg) ?(le_lt_trans gh)//=.
by near: x; apply: (cvgr_lt l); rewrite // ltrDl.
by near: x; apply: (cvgr_gt l); rewrite // gtrDl oppr_lt0.
Unshelve. all: end_near. Qed.

Lemma ger_cvgy f g : (\near a, f a <= g a) ->
f @ a --> +oo -> g @ a --> +oo.

Proof.

move=> uv /cvgryPge ucvg; apply/cvgryPge => A.
by near=> x do rewrite (le_trans _ (near uv x _))//.
Unshelve. all: end_near. Qed.

Lemma ler_cvgNy f g : (\near a, f a >= g a) ->
f @ a --> -oo -> g @ a --> -oo.

Proof.

move=> uv /cvgrNyPle ucvg; apply/cvgrNyPle => A.
by near=> x do rewrite (le_trans (near uv x _))//.
Unshelve. all: end_near. Qed.

End FilterRealType.

Section TopoProperFilterRealType.
Context {T : topologicalType} {a : set_system T} {Fa : ProperFilter a}.
Context {R : realFieldType}.
Implicit Types f g h : T -> R.

Lemma ler_cvg_to f g (l l' : R) : f @ a --> l -> g @ a --> l' ->
(\near a, f a <= g a) -> l <= l'.

Proof.

move=> fl gl; under eq_near do rewrite -subr_ge0; rewrite -subr_ge0.
by apply: cvgr_to_ge; apply: cvgB.
Qed.

Lemma ler_lim f g : cvg (f @ a) -> cvg (g @ a) ->
(\near a, f a <= g a) -> lim (f @ a) <= lim (g @ a).

Proof.

exact: ler_cvg_to. Qed.

End TopoProperFilterRealType.

Section FilterERealType.
Context {T : Type} {a : set_system T} {Fa : Filter a} {R : realFieldType}.
Local Open Scope ereal_scope.
Implicit Types f g h : T -> \bar R.

Lemma gee_cvgy f g : (\near a, f a <= g a) ->
f @ a --> +oo -> g @ a --> +oo.

Proof.

move=> uv /cvgeyPge uecvg; apply/cvgeyPge => A.
by near=> x do rewrite (le_trans _ (near uv x _))//.
Unshelve. all: end_near. Qed.

Lemma lee_cvgNy f g : (\near a, f a >= g a) ->
f @ a --> -oo -> g @ a --> -oo.

Proof.

move=> uv /cvgeNyPle uecvg; apply/cvgeNyPle => A.
by near=> x do rewrite (le_trans (near uv x _))//.
Unshelve. all: end_near. Qed.

Lemma squeeze_fin f g h : (\near a, f a <= g a <= h a) ->
(\near a, f a \is a fin_num) -> (\near a, h a \is a fin_num) ->
(\near a, g a \is a fin_num).

Proof.

apply: filterS3 => x /andP[fg gh].
rewrite !fin_numElt => /andP[oof _] /andP[_ hoo].
by rewrite (lt_le_trans oof) ?(le_lt_trans gh).
Qed.

Lemma squeeze_cvge f g h : (\near a, f a <= g a <= h a) ->
forall (l : \bar R), f @ a --> l -> h @ a --> l -> g @ a --> l.

Proof.

move=> fgh [l||]; last 2 first.
- by move=> + _; apply: gee_cvgy; apply: filterS fgh => ? /andP[].
- by move=> _; apply: lee_cvgNy; apply: filterS fgh => ? /andP[].
move=> /fine_cvgP[Ff fl] /fine_cvgP[Fh hl]; apply/fine_cvgP.
have Fg := squeeze_fin fgh Ff Fh; split=> //.
apply: squeeze_cvgr fl hl; near=> x => /=.
by have /(_ _)/andP[//|fg gh] := near fgh x; rewrite !fine_le//=; near: x.
Unshelve. all: end_near. Qed.

End FilterERealType.

Section TopoProperFilterERealType.
Context {T : topologicalType} {a : set_system T} {Fa : ProperFilter a}.
Context {R : realFieldType}.
Local Open Scope ereal_scope.
Implicit Types f g h : T -> \bar R.

Lemma lee_cvg_to f g l l' : f @ a --> l -> g @ a --> l' ->
(\near a, f a <= g a) -> l <= l'.

Proof.

move=> + + fg; move: l' l.
move=> /= [l'||] [l||]//=; rewrite ?leNye ?leey//=; first 1 last.
- by move=> /(gee_cvgy fg) /cvg_lim<-// /cvg_lim<-.
- by move=> /cvg_lim <-// /(lee_cvgNy fg) /cvg_lim<-.
- by move=> /(gee_cvgy fg) /cvg_lim<-// /cvg_lim<-.
move=> /fine_cvgP[Ff fl] /fine_cvgP[Fg gl].
rewrite lee_fin -(cvg_lim _ fl)// -(cvg_lim _ gl)//.
by apply: ler_lim; [apply: cvgP fl|apply: cvgP gl|near do apply: fine_le].
Unshelve. all: end_near. Qed.

Lemma lee_lim f g : cvg (f @ a) -> cvg (g @ a) ->
(\near a, f a <= g a) -> lim (f @ a) <= lim (g @ a).

Proof.

exact: lee_cvg_to. Qed.

End TopoProperFilterERealType.

Section Rhull.
Variable R : realType.

Definition Rhull (X : set R) : interval R := Interval
  (if `[< has_lbound X >] then BSide `[< X (inf X) >] (inf X)
                          else BInfty _ true)
  (if `[< has_ubound X >] then BSide (~~ `[< X (sup X) >]) (sup X)
                          else BInfty _ false).

Lemma Rhull0 : Rhull set0 = `]0, 0[ :> interval R.

Proof.

rewrite /Rhull (asboolT (has_lbound0 R)) (asboolT (has_ubound0 R)) asboolF //.
by rewrite sup0 inf0.
Qed.

Lemma sub_Rhull (X : set R) : X `<=` [set x | x \in Rhull X].

Proof.

move=> x Xx/=; rewrite in_itv/=.
case: (asboolP (has_lbound _)) => ?; case: (asboolP (has_ubound _)) => ? //=.
+ by case: asboolP => ?; case: asboolP => ? //=;
     rewrite !(lteifF,lteifT,sup_ubound,inf_lbound,sup_ub_strict,inf_lb_strict).
+ by case: asboolP => XinfX; rewrite !(lteifF, lteifT);
     [rewrite inf_lbound | rewrite inf_lb_strict].
+ by case: asboolP => XsupX; rewrite !(lteifF, lteifT);
     [rewrite sup_ubound | rewrite sup_ub_strict].
Qed.

Lemma is_intervalP (X : set R) : is_interval X <-> X = [set x | x \in Rhull X].

Proof.

split=> [iX|->]; last exact: interval_is_interval.
rewrite predeqE => x /=; split; [exact: sub_Rhull | rewrite in_itv/=].
case: (asboolP (has_lbound _)) => ?; case: (asboolP (has_ubound _)) => ? //=.
- case: asboolP => XinfX; case: asboolP => XsupX;
    rewrite !(lteifF, lteifT).
  + move=> /andP[]; rewrite le_eqVlt => /orP[/eqP <- //|infXx].
    rewrite le_eqVlt => /orP[/eqP -> //|xsupX].
    apply: (@interior_subset R).
    by rewrite interval_bounded_interior // /mkset infXx.
  + move=> /andP[]; rewrite le_eqVlt => /orP[/eqP <- //|infXx supXx].
    apply: (@interior_subset R).
    by rewrite interval_bounded_interior // /mkset infXx.
  + move=> /andP[infXx]; rewrite le_eqVlt => /orP[/eqP -> //|xsupX].
    apply: (@interior_subset R).
    by rewrite interval_bounded_interior // /mkset infXx.
  + move=> ?; apply: (@interior_subset R).
    by rewrite interval_bounded_interior // /mkset infXx.
- case: asboolP => XinfX; rewrite !(lteifF, lteifT, andbT).
  + rewrite le_eqVlt => /orP[/eqP<-//|infXx].
    apply: (@interior_subset R).
    by rewrite interval_right_unbounded_interior.
  + move=> infXx; apply: (@interior_subset R).
    by rewrite interval_right_unbounded_interior.
- case: asboolP => XsupX /=.
  + rewrite le_eqVlt => /orP[/eqP->//|xsupX].
    apply: (@interior_subset R).
    by rewrite interval_left_unbounded_interior.
  + move=> xsupX; apply: (@interior_subset R).
    by rewrite interval_left_unbounded_interior.
- by move=> _; rewrite (interval_unbounded_setT iX).
Qed.

Lemma connected_intervalP (E : set R) : connected E <-> is_interval E.

Proof.

split => [cE x y Ex Ey z /andP[xz zy]|].
- apply: contrapT => Ez.
  pose Az := E `&` [set x | x < z]; pose Bz := E `&` [set x | z < x].
  apply/connectedPn : cE; exists (fun b => if b then Az else Bz); split.
  + move: xz zy Ez.
    rewrite !le_eqVlt => /predU1P[<-//|xz] /predU1P[->//|zy] Ez.
    by case; [exists x | exists y].
  + rewrite /Az /Bz -setIUr; apply/esym/setIidPl => u Eu.
    by apply/orP; rewrite -neq_lt; apply/negP; apply: contraPnot Eu => /eqP <-.
  + split; [|rewrite setIC].
    + apply/disjoints_subset => /= u /closureI[_]; rewrite closure_gt => zu.
      by rewrite /Az setCI; right; apply/negP; rewrite -leNgt.
    + apply/disjoints_subset => /= u /closureI[_]; rewrite closure_lt => zu.
      by rewrite /Bz setCI; right; apply/negP; rewrite -leNgt.
- apply: contraPP => /connectedPn[A [A0 EU sepA]] intE.
  have [/= x A0x] := A0 false; have [/= y A1y] := A0 true.
  wlog xy : A A0 EU sepA x A0x y A1y / x < y.
    move=> /= wlog_hypo; have [xy|yx|{wlog_hypo}yx] := ltgtP x y.
    + exact: (wlog_hypo _ _ _ _ _ A0x _ A1y).
    + apply: (wlog_hypo (A \o negb) _ _ _ y _ x) => //=;
      by [rewrite setUC | rewrite separatedC].
    + move/separated_disjoint : sepA; rewrite predeqE => /(_ x)[] + _; apply.
      by split => //; rewrite yx.
  pose z := sup (A false `&` [set z | x <= z <= y]).
  have A1z : ~ (A true) z.
    have cA0z : closure (A false) z.
      suff : closure (A false `&` [set z | x <= z <= y]) z by case/closureI.
      apply: closure_sup; last by exists y => u [_] /andP[].
      by exists x; split => //; rewrite /mkset lexx /= (ltW xy).
    by move: sepA; rewrite /separated => -[] /disjoints_subset + _; apply.
  have /andP[xz zy] : x <= z < y.
    rewrite sup_ubound//=; [|by exists y => u [_] /andP[]|].
    + rewrite lt_neqAle sup_le_ub ?andbT; last by move=> u [_] /andP[].
      * by apply/negP; apply: contraPnot A1y => /eqP <-.
      * by exists x; split => //; rewrite /mkset /= lexx /= (ltW xy).
    + by split=> //; rewrite /mkset lexx (ltW xy).
  have [A0z|A0z] := pselect ((A false) z); last first.
  have {}xzy : x <= z <= y by rewrite xz ltW.
    have : ~ E z by rewrite EU => -[].
    by apply; apply (intE x y) => //; rewrite EU; [left|right].
  suff [z1 [/andP[zz1 z1y] Ez1]] : exists z1 : R, z <= z1 <= y /\ ~ E z1.
    apply Ez1; apply (intE x y) => //; rewrite ?EU; [by left|by right|].
    by rewrite z1y (le_trans _ zz1).
  have [r zcA1] : {r:{posnum R}| ball z r%:num `<=` ~` closure (A true)}.
    have ? : ~ closure (A true) z.
      by move: sepA; rewrite /separated => -[] _ /disjoints_subset; apply.
    have ? : open (~` closure (A true)) by exact/closed_openC/closed_closure.
    exact/nbhsC_ball/open_nbhs_nbhs.
  pose z1 : R := z + r%:num / 2; exists z1.
  have z1y : z1 <= y.
    rewrite leNgt; apply/negP => yz1.
    suff : (~` closure (A true)) y by apply; exact: subset_closure.
    apply zcA1; rewrite /ball /= ltr_distl (lt_le_trans zy) // ?lerDl //.
    rewrite andbT ltrBlDl addrC (lt_trans yz1) // ltrD2l.
    by rewrite ltr_pdivrMr // ltr_pMr // ltr1n.
  rewrite z1y andbT lerDl; split => //.
  have ncA1z1 : (~` closure (A true)) z1.
    apply zcA1; rewrite /ball /= /z1 opprD addNKr normrN.
    by rewrite ger0_norm // ltr_pdivrMr // ltr_pMr // ltr1n.
  have nA0z1 : ~ (A false) z1.
    move=> A0z1; have : z < z1 by rewrite /z1 ltrDl.
    apply/negP; rewrite -leNgt.
     apply: sup_ubound; first by exists y => u [_] /andP[].
    by split => //; rewrite /mkset /z1 (le_trans xz) /= ?lerDl // (ltW z1y).
  by rewrite EU => -[//|]; apply: contra_not ncA1z1; exact: subset_closure.
Qed.

Lemma set_itvK : {in neitv, cancel pred_set Rhull}.

Proof.

move=> [[[] x|[]] [[] y|[]]] /neitvP //;
  rewrite /Rhull /= !(in_itv, inE)/= ?bnd_simp => xy.
- rewrite asboolT// inf_itv// lexx/= xy asboolT// asboolT//=.
  by rewrite asboolF//= sup_itv//= ltxx ?andbF.
- by rewrite asboolT// inf_itv// ?asboolT// ?sup_itv// ?lexx ?xy.
- by rewrite asboolT//= inf_itv// lexx asboolT// asboolF.
- rewrite asboolT// inf_itv//= ltxx asboolF// asboolT//.
  by rewrite sup_itv// ltxx andbF asboolF.
  rewrite asboolT // inf_itv // ltxx asboolF // asboolT //.
  by rewrite sup_itv // xy lexx asboolT.
- by rewrite asboolT // inf_itv// ltxx asboolF // asboolF.
- by rewrite asboolF // asboolT // sup_itv// ltxx asboolF.
- by rewrite asboolF // asboolT // sup_itv// lexx asboolT.
- by rewrite asboolF // asboolF.
Qed.

Lemma RhullT : Rhull setT = `]-oo, +oo[%R :> interval R.

Proof.

by rewrite /Rhull -set_itvNyy asboolF// asboolF. Qed.

Lemma RhullK : {in (@is_interval _ : set (set R)), cancel Rhull pred_set}.

Proof.

by move=> X /asboolP iX; exact/esym/is_intervalP. Qed.

Lemma set_itv_setT (i : interval R) : [set` i] = setT -> i = `]-oo, +oo[.

Proof.

have [i0 /(congr1 Rhull)|] := boolP (neitv i).
by rewrite set_itvK// => ->; exact: RhullT.
by rewrite negbK => /eqP ->; rewrite predeqE => /(_ 0)[_]/(_ Logic.I).
Qed.

Lemma Rhull_smallest A : [set` Rhull A] = smallest (@is_interval R) A.

Proof.

apply/seteqP; split; last first.
  by apply: smallest_sub; [apply: interval_is_interval | apply: sub_Rhull].
move=> x /= + I [Iitv AI]; rewrite /Rhull.
have [|] := asboolP (has_lbound A) => lA; last first.
  have /forallNP/(_ x)/existsNP[a] := lA.
  move=> /existsNP[Aa /negP]; rewrite -ltNge => ax.
  have [|]:= asboolP (has_ubound A) => uA; last first.
    move=> ?; have /forallNP/(_ x)/existsNP[b] := uA.
    move=> /existsNP[Ab /negP]; rewrite -ltNge => xb.
    have /is_intervalPlt/(_ a b) := Iitv; apply; do ?by apply: AI.
    by rewrite ax xb.
  have [As|NAs]/= := asboolP (A _) => xA.
    by apply: (Iitv a (sup A)); by [apply: AI | rewrite ltW ?ax].
  have [||b Ab xb] := @sup_gt _ A x; do ?by [exists a | rewrite (itvP xA)].
  have /is_intervalPlt/(_ a b) := Iitv; apply; do ?by apply: AI.
  by rewrite ax xb.
have [|]:= asboolP (has_ubound A) => uA; last first.
  have /forallNP/(_ x)/existsNP[b] := uA.
  move=> /existsNP[Ab /negP]; rewrite -ltNge => xb.
  have [Ai|NAi]/= := asboolP (A _) => xA.
    by apply: (Iitv (inf A) b); by [apply: AI | rewrite (ltW xb)].
  have [||a Aa ax] := @inf_lt _ A x; do ?by [exists b | rewrite (itvP xA)].
  have /is_intervalPlt/(_ a b) := Iitv; apply; do ?by apply: AI.
  by rewrite ax xb.
have [Ai|NAi]/= := asboolP (A _); have [As|NAs]/= := asboolP (A _).
- by apply: Iitv; apply: AI.
- move=> xA.
  have [||b Ab xb] := @sup_gt _ A x; do ?by [exists (inf A) | rewrite (itvP xA)].
  have /(_ (inf A) b) := Iitv; apply; do ?by apply: AI.
  by rewrite (itvP xA) (ltW xb).
- move=> xA.
  have [||a Aa ax] := @inf_lt _ A x; do ?by [exists (sup A) | rewrite (itvP xA)].
  have /(_ a (sup A)) := Iitv; apply; do ?by apply: AI.
  by rewrite (itvP xA) (ltW ax).
have [->|/set0P AN0] := eqVneq A set0.
  by rewrite inf0 sup0 itv_ge//= ltBSide/= ltxx.
move=> xA.
have [||a Aa ax] := @inf_lt _ A x; do ?by [|rewrite (itvP xA)].
have [||b Ab xb] := @sup_gt _ A x; do ?by [|rewrite (itvP xA)].
have /is_intervalPlt/(_ a b) := Iitv; apply; do ?by apply: AI.
by rewrite ax xb.
Qed.

Lemma le_Rhull : {homo Rhull : A B / (A `<=` B) >-> {subset A <= B}}.

Proof.

move=> A B AB; suff: [set` Rhull A] `<=` [set` Rhull B] by [].
rewrite Rhull_smallest; apply: smallest_sub; first exact: interval_is_interval.
by rewrite Rhull_smallest; apply: sub_smallest.
Qed.

Lemma neitv_Rhull A : ~~ neitv (Rhull A) -> A = set0.

Proof.

move/negPn/eqP => A0; rewrite predeqE => r; split => // /sub_Rhull.
by rewrite A0.
Qed.

Lemma Rhull_involutive A : Rhull [set` Rhull A] = Rhull A.

Proof.

have [A0|/neitv_Rhull] := boolP (neitv (Rhull A)); first by rewrite set_itvK.
by move=> ->; rewrite ?Rhull0 set_itvE Rhull0.
Qed.

Lemma disj_itv_Rhull (A B : set R) : A `&` B = set0 ->
is_interval A -> is_interval B -> disjoint_itv (Rhull A) (Rhull B).

Proof.

by move=> AB0 iA iB; rewrite /disjoint_itv RhullK ?inE// RhullK ?inE.
Qed.

End Rhull.

properties of segments in $\bar{R}$

Section segment.
Context {R : realType}.

Lemma segment_connected (a b : R) : connected `[a, b].

Proof.

exact/connected_intervalP/interval_is_interval. Qed.

Lemma segment_compact (a b : R) : compact `[a, b].

Proof.

have [leab|ltba] := lerP a b; last first.
  by move=> F FF /filter_ex [x abx]; move: ltba; rewrite (itvP abx).
rewrite compact_cover => I D f fop sabUf.
set B := [set x | exists2 E : {fset I}, {subset E <= D} &
  `[a, x] `<=` \bigcup_(i in [set` E]) f i /\ (\bigcup_(i in [set` E]) f i) x].
set A := `[a, b] `&` B.
suff Aeab : A = `[a, b]%classic.
  suff [_ [E ? []]] : A b by exists E.
  by rewrite Aeab/= inE/=; exact/andP.
apply: segment_connected.
- have aba : a \in `[a, b] by rewrite in_itv /= lexx.
  exists a; split=> //; have /sabUf [i /= Di fia] := aba.
  exists [fset i]%fset; first by move=> ?; rewrite inE inE => /eqP->.
  split; last by exists i => //=; rewrite inE.
  move=> x /= aex; exists i; [by rewrite /= inE|suff /eqP-> : x == a by []].
  by rewrite eq_le !(itvP aex).
- exists B => //; rewrite openE => x [E sD [saxUf [i Di fx]]].
  have : open (f i) by have /sD := Di; rewrite inE => /fop.
  rewrite openE => /(_ _ fx) [e egt0 xe_fi]; exists e => // y xe_y.
  exists E => //; split; last by exists i => //; apply/xe_fi.
  move=> z /= ayz; have [lezx|ltxz] := lerP z x.
    by apply/saxUf; rewrite /= in_itv/= (itvP ayz) lezx.
  exists i => //; apply/xe_fi; rewrite /ball_/= distrC ger0_norm.
    have lezy : z <= y by rewrite (itvP ayz).
    rewrite ltrBlDl; apply: le_lt_trans lezy _; rewrite -ltrBlDr.
    by have := xe_y; rewrite /ball_ => /ltr_distlCBl.
  by rewrite subr_ge0; apply/ltW.
exists A; last by rewrite predeqE => x; split=> [[] | []].
move=> x clAx; have abx : x \in `[a, b].
  by apply: interval_closed; have /closureI [] := clAx.
split=> //; have /sabUf [i Di fx] := abx.
have /fop := Di; rewrite openE => /(_ _ fx) [_ /posnumP[e] xe_fi].
have /clAx [y [[aby [E sD [sayUf _]]] xe_y]] :=
  nbhsx_ballx x e%:num ltac:(by []).
exists (i |` E)%fset; first by move=> j /fset1UP[->|/sD] //; rewrite inE.
split=> [z axz|]; last first.
  exists i; first by rewrite /= !inE eq_refl.
  by apply/xe_fi; rewrite /ball_/= subrr normr0.
have [lezy|ltyz] := lerP z y.
  have /sayUf [j Dj fjz] : z \in `[a, y] by rewrite in_itv /= (itvP axz) lezy.
  by exists j => //=; rewrite inE orbC Dj.
exists i; first by rewrite /= !inE eq_refl.
apply/xe_fi; rewrite /ball_/= ger0_norm; last by rewrite subr_ge0 (itvP axz).
rewrite ltrBlDl -ltrBlDr; apply: lt_trans ltyz.
by apply: ltr_distlCBl; rewrite distrC.
Qed.

End segment.

Lemma IVT (R : realType) (f : R -> R) (a b v : R) :
  a <= b -> {within `[a, b], continuous f} ->
  minr (f a) (f b) <= v <= maxr (f a) (f b) ->
  exists2 c, c \in `[a, b] & f c = v.

Proof.

move=> leab fcont; gen have ivt : f v fcont / f a <= v <= f b ->
    exists2 c, c \in `[a, b] & f c = v; last first.
  case: (leP (f a) (f b)) => [] _ fabv /=; first exact: ivt.
  have [| |c cab /oppr_inj] := ivt (- f) (- v); last by exists c.
  - by move=> x /=; apply/continuousN/fcont.
  - by rewrite lerNr opprK lerNr opprK andbC.
move=> favfb; suff: is_interval (f @` `[a,b]).
  apply; last exact: favfb.
  - by exists a => //=; rewrite in_itv/= lexx.
  - by exists b => //=; rewrite in_itv/= leab lexx.
apply/connected_intervalP/connected_continuous_connected => //.
exact: segment_connected.
Qed.

Section prod_NormedModule.
Context {K : numFieldType} {U V : normedModType K}.

Lemma prod_norm_scale (l : K) (x : U * V) : `| l *: x | = `|l| * `| x |.

Proof.

by rewrite prod_normE /= !normrZ maxr_pMr. Qed.

HB.instance Definition _ :=
  PseudoMetricNormedZmod_Tvs_isNormedModule.Build K (U * V)%type
  prod_norm_scale.

End prod_NormedModule.

Section prod_NormedModule_lemmas.
Context {T : Type} {K : numDomainType} {U V : normedModType K}.

Lemma fcvgr2dist_ltP {F : set_system U} {G : set_system V}
  {FF : Filter F} {FG : Filter G} (y : U) (z : V) :
  (F, G) --> (y, z) <->
  forall eps, 0 < eps ->
   \forall y' \near F & z' \near G, `| (y, z) - (y', z') | < eps.

Proof.

exact: fcvgrPdist_lt. Qed.

Lemma cvgr2dist_ltP {I J} {F : set_system I} {G : set_system J}
  {FF : Filter F} {FG : Filter G} (f : I -> U) (g : J -> V) (y : U) (z : V) :
  (f @ F, g @ G) --> (y, z) <->
  forall eps, 0 < eps ->
   \forall i \near F & j \near G, `| (y, z) - (f i, g j) | < eps.

Proof.

rewrite fcvgr2dist_ltP; split=> + e e0 => /(_ e e0);
by rewrite !near_simpl// => ?; rewrite !near_simpl.
Qed.

Lemma cvgr2dist_lt {I J} {F : set_system I} {G : set_system J}
  {FF : Filter F} {FG : Filter G} (f : I -> U) (g : J -> V) (y : U) (z : V) :
  (f @ F, g @ G) --> (y, z) ->
  forall eps, 0 < eps ->
   \forall i \near F & j \near G, `| (y, z) - (f i, g j) | < eps.

Proof.

by rewrite cvgr2dist_ltP. Qed.

End prod_NormedModule_lemmas.
Arguments cvgr2dist_ltP {_ _ _ _ _ F G FF FG}.
Arguments cvgr2dist_lt {_ _ _ _ _ F G FF FG}.

Lemma bounded_locally (T : topologicalType)
(R : numFieldType) (V : normedModType R) (A : set T) (f : T -> V) :
[bounded f x | x in A] -> [locally [bounded f x | x in A]].

Proof.

by move=> /sub_boundedr AB x Ax; apply: AB; apply: within_nbhsW. Qed.

Notation "k .-lipschitz_on f" :=
  (dominated_by (self_sub id) k (self_sub f)) : type_scope.

Lemma sub_klipschitz (K : numFieldType) (V W : normedModType K) (k : K)
    (f : V -> W) (F G : set_system (V * V)) :
  F `=>` G -> k.-lipschitz_on f G -> k.-lipschitz_on f F.

Proof.

exact. Qed.

Definition lipschitz_on (K : numFieldType) (V W : normedModType K)
           (f : V -> W) (F : set_system (V * V)) :=
  \forall M \near +oo, M.-lipschitz_on f F.

Lemma sub_lipschitz (K : numFieldType) (V W : normedModType K)
    (f : V -> W) (F G : set_system (V * V)) :
  F `=>` G -> lipschitz_on f G -> lipschitz_on f F.

Proof.

by move=> FG; rewrite /lipschitz_on; apply: filterS => M; apply: FG. Qed.

Lemma klipschitzW (K : numFieldType) (V W : normedModType K) (k : K)
(f : V -> W) (F : set_system (V * V)) {PF : ProperFilter F} :
k.-lipschitz_on f F -> lipschitz_on f F.

Proof.

by move=> f_lip; apply/ex_dom_bound; exists k. Qed.

Notation "k .-lipschitz_ A f" :=
  (k.-lipschitz_on f (globally (A `*` A))) : type_scope.
Notation "k .-lipschitz f" := (k.-lipschitz_setT f) : type_scope.
Notation "[ 'lipschitz' E | x 'in' A ]" :=
  (lipschitz_on (fun x => E) (globally (A `*` A))) : type_scope.
Notation lipschitz f := [lipschitz f x | x in setT].

Lemma lipschitz_set0 (K : numFieldType) (V W : normedModType K)
  (f : V -> W) : [lipschitz f x | x in set0].

Proof.

by apply: nearW; rewrite setX0 => ?; apply: globally0. Qed.

Lemma lipschitz_set1 (K : numFieldType) (V W : normedModType K)
(f : V -> W) (a : V) : [lipschitz f x | x in [set a]].

Proof.

apply: (@klipschitzW _ _ _ `|f a|).
exact: (@globally_properfilter _ _ (a, a)).
by move=> [x y] /= [] -> ->; rewrite !subrr !normr0 mulr0.
Qed.

Lemma klipschitz_locally (R : numFieldType) (V W : normedModType R) (k : R)
(f : V -> W) (A : set V) :
k.-lipschitz_A f -> [locally k.-lipschitz_A f].

Proof.

by move=> + x Ax; apply: sub_klipschitz; apply: within_nbhsW. Qed.

Lemma lipschitz_locally (R : numFieldType) (V W : normedModType R)
(A : set V) (f : V -> W) :
[lipschitz f x | x in A] -> [locally [lipschitz f x | x in A]].

Proof.

by move=> + x Ax; apply: sub_lipschitz; apply: within_nbhsW. Qed.

Lemma lipschitz_id (R : numFieldType) (V : normedModType R) :
1.-lipschitz (@id V).

Proof.

by move=> [/= x y] _; rewrite mul1r. Qed.

Arguments lipschitz_id {R V}.

Section LinearContinuousBounded.
Variables (R : numFieldType) (V W : normedModType R).

Lemma linear_boundedP (f : {linear V -> W}) : bounded_near f (nbhs 0) <->
\forall r \near +oo, forall x, `|f x| <= r * `|x|.

Proof.

split=> [|/pinfty_ex_gt0 [r r0 Bf]]; last first.
  apply/ex_bound; exists r; apply/nbhs_norm0P; exists 1 => //= x /=.
  by rewrite -(gtr_pMr _ r0) => /ltW; exact/le_trans/Bf.
rewrite /bounded_near => /pinfty_ex_gt0 [M M0 /nbhs_norm0P [_/posnumP[e] efM]].
near (0 : R)^'+ => d; near=> r => x.
have[->|x0] := eqVneq x 0; first by rewrite raddf0 !normr0 mulr0.
have nd0 : d / `|x| > 0 by rewrite divr_gt0 ?normr_gt0.
have: `|f (d / `|x| *: x)| <= M.
  by apply: efM => /=; rewrite normrZ gtr0_norm// divfK ?normr_eq0//.
rewrite linearZ/= normrZ gtr0_norm// -ler_pdivlMl//; move/le_trans; apply.
rewrite invfM invrK mulrAC ler_wpM2r//; near: r; apply: nbhs_pinfty_ge.
by rewrite rpredM// ?rpredV ?gtr0_real.
Unshelve. all: by end_near. Qed.

Lemma continuous_linear_bounded (x : V) (f : {linear V -> W}) :
{for 0, continuous f} -> bounded_near f (nbhs x).

Proof.

rewrite /prop_for/continuous_at linear0 /bounded_near => f0.
near=> M; apply/nbhs0P.
near do rewrite /= linearD (le_trans (ler_normD _ _))// -lerBrDl.
by apply: cvgr0_norm_le; rewrite // subr_gt0.
Unshelve. all: by end_near. Qed.

Lemma bounded_linear_continuous (f : {linear V -> W}) :
bounded_near f (nbhs (0 : V)) -> continuous f.

Proof.

move=> /linear_boundedP [y [yreal fr]] x; near +oo_R => r.
apply/(@cvgrPdist_lt _ _ _ (nbhs x)) => e e_gt0; near=> z; rewrite -linearB.
rewrite (le_lt_trans (fr r _ _))// -?ltr_pdivlMl//.
by near: z; apply: cvgr_dist_lt => //; rewrite mulrC divr_gt0.
Unshelve. all: by end_near. Qed.

Lemma continuousfor0_continuous (f : {linear V -> W}) :
{for 0, continuous f} -> continuous f.

Proof.

by move=> /continuous_linear_bounded/bounded_linear_continuous. Qed.

Lemma linear_bounded_continuous (f : {linear V -> W}) :
bounded_near f (nbhs 0) <-> continuous f.

Proof.

split; first exact: bounded_linear_continuous.
by move=> /(_ 0); exact: continuous_linear_bounded.
Qed.

Lemma bounded_funP (f : {linear V -> W}) :
(forall r, exists M, forall x, `|x| <= r -> `|f x| <= M) <->
bounded_near f (nbhs (0 : V)).

Proof.

split => [/(_ 1) [M Bf]|/linear_boundedP fr y].
apply/ex_bound; exists M; apply/nbhs_normP => /=; exists 1 => //= x /=.
by rewrite sub0r normrN => x1; exact/Bf/ltW.
near +oo_R => r; exists (r * y) => x xe.
rewrite (@le_trans _ _ (r * `|x|)) //; first by move: {xe} x; near: r.
by rewrite ler_pM.
Unshelve. all: by end_near. Qed.

End LinearContinuousBounded.

Section contractions.
Context {R : numDomainType} {X Y : normedModType R} {U : set X} {V : set Y}.

Definition contraction (q : {nonneg R}) (f : {fun U >-> V}) :=
  q%:num < 1 /\ q%:num.-lipschitz_U f.

Definition is_contraction (f : {fun U >-> V}) := exists q, contraction q f.

End contractions.

Lemma contraction_fixpoint_unique {R : realDomainType}
    {X : normedModType R} (U : set X) (f : {fun U >-> U}) (x y : X) :
  is_contraction f -> U x -> U y -> x = f x -> y = f y -> x = y.

Proof.

Section cvg_seq_bounded.
Context {K : numFieldType}.
Local Notation "'+oo'" := (@pinfty_nbhs K).

Lemma cvg_seq_bounded {V : normedModType K} (a : nat -> V) :
cvgn a -> bounded_fun a.

Proof.

move=> /cvg_bounded/ex_bound => -[/= Moo] => -[N _ /(_ _) aM].
have Moo_real : Moo \is Num.real by rewrite ger0_real ?(le_trans _ (aM N _))/=.
rewrite /bounded_near /=; near=> M => n _.
have [nN|nN]/= := leqP N n; first by apply: (le_trans (aM _ _)).
move: n nN; suff /(_ (Ordinal _)) : forall n : 'I_N, `|a n| <= M by [].
by near: M; apply: filter_forall => i; apply: nbhs_pinfty_ge.
Unshelve. all: by end_near. Qed.

End cvg_seq_bounded.

Lemma compact_bounded (K : realType) (V : normedModType K) (A : set V) :
compact A -> bounded_set A.

Proof.

rewrite compact_cover => Aco.
have covA : A `<=` \bigcup_(n : int) [set p | `|p| < n%:~R].
  by move=> p _; exists (floor `|p| + 1) => //=; rewrite floorD1_gt.
have /Aco [] := covA.
  move=> n _; rewrite openE => p; rewrite /= -subr_gt0 => ltpn.
  apply/nbhs_ballP; exists (n%:~R - `|p|) => // q.
  rewrite -ball_normE /= ltrBrDr distrC; apply: le_lt_trans.
  by rewrite -{1}(subrK p q) ler_normD.
move=> D _ DcovA.
exists (\big[maxr/0]_(i : D) (fsval i)%:~R).
rewrite bigmax_real//; split=> // x ltmaxx p /DcovA [n Dn /lt_trans /(_ _)/ltW].
apply; apply: le_lt_trans ltmaxx.
have : n \in enum_fset D by [].
by rewrite enum_fsetE => /mapP[/= i iD ->]; exact/le_bigmax.
Qed.

Section Closed_Ball_normedModType.

Lemma closed_closed_ball_ (R : realFieldType) (V : normedModType R)
(x : V) (e : R) : closed (closed_ball_ normr x e).

Proof.

rewrite /closed_ball_ -/((normr \o (fun y => x - y)) @^-1` [set x | x <= e]).
apply: (closed_comp _ (@closed_le _ _)) => y _.
apply: (continuous_comp _ (@norm_continuous _ _ _)).
exact: (continuousB (@cst_continuous _ _ _ _)).
Qed.

Lemma closed_ballE (R : realFieldType) (V : normedModType R) (x : V)
(r : R) : 0 < r -> closed_ball x r = closed_ball_ normr x r.

Proof.

move=> /posnumP[e]; rewrite eqEsubset; split => y.
  rewrite /closed_ball closureE; apply; split; first exact: closed_closed_ball_.
  by move=> z; rewrite -ball_normE; exact: ltW.
have [-> _|xy] := eqVneq x y; first exact: closed_ballxx.
rewrite /closed_ball closureE -ball_normE.
rewrite /closed_ball_ /= le_eqVlt.
move => /orP[/eqP xye B [Bc Be]|xye _ [_ /(_ _ xye)]//].
apply: Bc => B0 /nbhs_ballP[s s0] B0y.
have [es|se] := leP s e%:num; last first.
  exists x; split; first by apply: Be; rewrite ball_normE; apply: ballxx.
  by apply: B0y; rewrite -ball_normE /ball_ /= distrC xye.
exists (y + (s / 2) *: (`|x - y|^-1 *: (x - y))); split; [apply: Be|apply: B0y].
  rewrite /= opprD addrA -[X in `|X - _|](scale1r (x - y)) scalerA -scalerBl.
  rewrite -[X in X - _](@divrr _ `|x - y|) ?unitfE ?normr_eq0 ?subr_eq0//.
  rewrite -mulrBl -scalerA normrZ normfZV ?subr_eq0// mulr1.
  rewrite gtr0_norm; first by rewrite ltrBlDl xye ltrDr mulr_gt0.
  by rewrite subr_gt0 xye ltr_pdivrMr // mulr_natr mulr2n ltr_pwDl.
rewrite -ball_normE /ball_ /= opprD addrA addrN add0r normrN normrZ.
rewrite normfZV ?subr_eq0// mulr1 normrM (gtr0_norm s0) gtr0_norm //.
by rewrite ltr_pdivrMr // ltr_pMr // ltr1n.
Qed.

Lemma closed_ball_itv (R : realFieldType) (x r : R) : 0 < r ->
closed_ball x r = `[x - r, x + r]%classic.

Proof.

by move=> r0; apply/seteqP; split => y;
rewrite closed_ballE// /closed_ball_ /= in_itv/= ler_distlC.
Qed.

Lemma closed_ball_ball {R : realFieldType} (x r : R) : 0 < r ->
closed_ball x r = [set x - r] `|` ball x r `|` [set x + r].

Proof.

move=> r0; rewrite closed_ball_itv// -(@setU1itv _ _ _ (x - r)); last first.
by rewrite bnd_simp lerBlDr -addrA lerDl ltW// addr_gt0.
rewrite -(@setUitv1 _ _ _ (x + r)); last first.
by rewrite bnd_simp ltrBlDr -addrA ltrDl addr_gt0.
by rewrite ball_itv setUA.
Qed.

Lemma closed_ballR_compact (R : realType) (x e : R) : 0 < e ->
compact (closed_ball x e).

Proof.

move=> e_gt0; have : compact `[x - e, x + e] by apply: segment_compact.
by rewrite closed_ballE//; under eq_set do rewrite in_itv -ler_distlC.
Qed.

Lemma closed_ball_subset (R : realFieldType) (M : normedModType R) (x : M)
(r0 r1 : R) : 0 < r0 -> r0 < r1 -> closed_ball x r0 `<=` ball x r1.

Proof.

move=> r00 r01; rewrite (_ : r0 = (PosNum r00)%:num) // closed_ballE //.
by move=> m xm; rewrite -ball_normE /ball_ /= (le_lt_trans _ r01).
Qed.

Lemma nbhs_closedballP (R : realFieldType) (M : normedModType R) (B : set M)
(x : M) : nbhs x B <-> exists r : {posnum R}, closed_ball x r%:num `<=` B.

Proof.

split=> [/nbhs_ballP[_/posnumP[r] xrB]|[e xeB]]; last first.
apply/nbhs_ballP; exists e%:num => //=.
exact: (subset_trans (@subset_closure _ _) xeB).
exists (r%:num / 2)%:itv.
apply: (subset_trans (closed_ball_subset _ _) xrB) => //=.
by rewrite lter_pdivrMr // ltr_pMr // ltr1n.
Qed.

Lemma open_subball {R : numFieldType} {M : normedModType R} (A : set M)
(x : M) : open A -> A x -> \forall e \near 0^'+, ball x e `<=` A.

Proof.

move=> oA Ax; have /nbhsr0P/= : nbhs x A by exact/open_nbhs_nbhs.
apply: filterS => e xeA y exy; apply: xeA.
by rewrite -ball_normE/= in exy; exact: ltW.
Qed.

Lemma closed_disjoint_closed_ball {R : realFieldType} {M : normedModType R}
(K : set M) z : closed K -> ~ K z ->
\forall d \near 0^'+, closed_ball z d `&` K = set0.

Proof.

rewrite -openC => /open_subball /[apply]; move=> [e /= e0].
move=> /(_ (e / 2)) /= ; rewrite sub0r normrN gtr0_norm ?divr_gt0//.
rewrite ltr_pdivrMr// ltr_pMr// ltr1n => /(_ erefl isT).
move/subsets_disjoint; rewrite setCK => ze2K0.
exists (e / 2); first by rewrite /= divr_gt0.
move=> x /= + x0; rewrite sub0r normrN gtr0_norm// => xe.
by move: ze2K0; apply: subsetI_eq0 => //=; exact: closed_ball_subset.
Qed.

Lemma locally_compactR (R : realType) : locally_compact [set: R].

Proof.

move=> x _; rewrite withinET; exists (closed_ball x 1).
by apply/nbhs_closedballP; exists 1%:pos.
by split; [apply: closed_ballR_compact | apply: closed_ball_closed].
Qed.

Lemma interior_closed_ballE (R : realType) (V : normedModType R) (x : V)
(r : R) : 0 < r -> (closed_ball x r)° = ball x r.

Proof.

move=> r0; rewrite eqEsubset; split; last first.
  by rewrite -open_subsetE; [exact: subset_closure | exact: ball_open].
move=> /= t; rewrite closed_ballE // /interior /= -nbhs_ballE => [[]] s s0.
have [-> _|nxt] := eqVneq t x; first exact: ballxx.
near ((0 : R^o)^') => e; rewrite -ball_normE /closed_ball_ => tsxr.
pose z := t + `|e| *: (t - x); have /tsxr /= : `|t - z| < s.
  rewrite distrC addrAC subrr add0r normrZ normr_id.
  rewrite -ltr_pdivlMr ?(normr_gt0,subr_eq0) //.
  by near: e; apply/dnbhs0_lt; rewrite divr_gt0 // normr_gt0 subr_eq0.
rewrite /z opprD addrA -scalerN -{1}(scale1r (x - t)) opprB -scalerDl normrZ.
apply lt_le_trans; rewrite ltr_pMl; last by rewrite normr_gt0 subr_eq0 eq_sym.
by rewrite ger0_norm // ltrDl normr_gt0; near: e; exists 1 => /=.
Unshelve. all: by end_near. Qed.

Lemma open_nbhs_closed_ball (R : realType) (V : normedModType R) (x : V)
(r : R) : 0 < r -> open_nbhs x (closed_ball x r)°.

Proof.

move=> r0; split; first exact: open_interior.
by rewrite interior_closed_ballE //; exact: ballxx.
Qed.

End Closed_Ball_normedModType.

Files

Module mathcomp.analysis.normedtype_theory.normed_module