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@hoheinzollern hoheinzollern commented May 27, 2024

This PR will be rebased on PR #1506 (or on master should the latter be merged before).

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The CI error is:

       > COQC theories/lspace.v
       > File "./theories/lspace.v", line 82, characters 33-42:
       > Error: Syntax error: [reduce] expected after ':=' (in [def_body]).

@hoheinzollern
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Wikipedia uses the p-norm to define Lp spaces when p may be +oo, whereas for example this reference sticks to the definition that was previously in this PR. Klenke also seems to go with the Wikipedia approach.
I have now moved to using norms in the last commits, and extending the theory to extended reals.
Is there a good reason to choose one over the other?

Comment on lines +157 to +161
match p with
| r%:E => [get q : R | r^-1 + q^-1 = 1]%:E
| +oo => 1
| -oo => 0
end.
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This is ill-defined when p = 1, writing the following

Suggested change
match p with
| r%:E => [get q : R | r^-1 + q^-1 = 1]%:E
| +oo => 1
| -oo => 0
end.
[get q : \bar R | (q > 0) /\ r^-1 + q^-1 = 1]

with a proper definition of ^-1 that I might PR soon.

Comment on lines 248 to 260
Lemma ess_sup_cst_lty r : (0 < mu setT)%E -> (ess_sup mu (cst r) < +oo)%E.
Proof.
rewrite /ess_sup => mu0.
under eq_set do rewrite preimage_cst/=.
rewrite ereal_inf_EFin ?ltry//.
- exists r => x/=; case: ifPn => [_|].
by move: mu0 => /[swap] ->; rewrite ltNge lexx.
by rewrite set_itvE notin_setE//= ltNge => /negP/negbNE.
by exists r => /=; rewrite ifF//; rewrite set_itvE;
rewrite memNset //=; apply/negP; rewrite -real_leNgt ?num_real.
Qed.

Lemma ess_sup_cst r : (0 < mu setT)%E -> (ess_sup mu (cst r) = r%:E)%E.
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The former lemma is subsumed by the latter.

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no need to have it indeed

Qed.


Lemma Lnorm_eq0 (f : ty) : nm f = 0 -> f = 0 %[ae mu].
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@CohenCyril CohenCyril Feb 7, 2025

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Add a lemma saying forall f : ty, nm f = 'N[mu]_p[f]%:E

Comment on lines +4114 to +4134
Require Import -(notations) Setoid.

Declare Scope signature_scope.
Delimit Scope signature_scope with signature.
Import -(notations) Morphisms.
Module ProperNotations.

Notation " R ++> R' " := (@respectful _ _ (R%signature) (R'%signature))
(right associativity, at level 55) : signature_scope.

Notation " R ==> R' " := (@respectful _ _ (R%signature) (R'%signature))
(right associativity, at level 55) : signature_scope.

Notation " R ~~> R' " := (@respectful _ _ (Program.Basics.flip (R%signature)) (R'%signature))
(right associativity, at level 55) : signature_scope.

End ProperNotations.
Import ProperNotations.

Arguments Proper {A}%_type R%_signature m.
Arguments respectful {A B}%_type (R R')%_signature _ _.
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This should be in a dedicated compat file for importing setoid rewrite into MCA.

Comment on lines +5361 to +5362
Lemma ess_supP f a :
ess_sup f = a <-> \forall x \ae mu, (f x)%:E <= a.
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Suggested change
Lemma ess_supP f a :
ess_sup f = a <-> \forall x \ae mu, (f x)%:E <= a.
Lemma ess_supP f a :
reflect (\forall x \ae mu, (f x)%:E <= a) (ess_sup f <= a).

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@hoheinzollern I can try to contribute this lemma if you haven't done it somewhere else.

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This is the main theorem about essential supremums i.e. "ess_sup ⊣ (<=_ae)", and essentially everything comes from this

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affeldt-aist commented Jul 1, 2025

(deleted comment)

@affeldt-aist affeldt-aist reopened this Jul 1, 2025
@hoheinzollern
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I can see there was activity. Shall I close this PR? It looks no longer relevant.

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I closed it by mistake. I think that it should be rebased on top of master because iirc it was going a step further by using a feature of MathComp that was only available in master.

@affeldt-aist affeldt-aist added the experiment 🧪 This issue/PR is very experimental label Jul 3, 2025
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