sigma-rings (math-comp#1222)

sigma-rings

Co-authored-by: @TheoWinterhalter
Co-authored-by: @JeremyDubut
Co-authored-by: @AkihisaYamada
Co-authored-by: @proux01

CHANGELOG_UNRELEASED.md

@@ -33,6 +33,29 @@
 
 - in `normedtype.v`:
   + lemma `not_near_at_leftP`
+- in `classical_sets.v`:
+  + lemmas `setD_bigcup`, `nat_nonempty`
+  + hint `nat_nonempty`
+
+- in `measure.v`:
+  + structure `SigmaRing`, notation `sigmaRingType`
+  + factory `isSigmaRing`
+  + lemma `bigcap_measurable` for `sigmaRingType`
+  + lemma `setDI_semi_setD_closed`
+  + lemmas `powerset_lambda_system`, `lambda_system_smallest`, `sigmaRingType_lambda_system`
+  + definitions `niseq_closed`, `sigma_ring` (notation `<<sr _ >>`),
+    `monotone` (notation `<<M _ >>`)
+  + lemmas `smallest_sigma_ring`, `sigma_ring_monotone`, `g_sigma_ring_monotone`,
+    `sub_g_sigma_ring`, `setring_monotone_sigma_ring`, `g_monotone_monotone`,
+	`g_monotone_setring`, `g_monotone_g_sigma_ring`, `monotone_setring_sub_g_sigma_ring`
+
+- in `classical_sets.v`:
+  + lemma `bigcup_bigsetU_bigcup`
+  + lemmas `setDUD`, `setIDAC`
+
+- in `measure.v`:
+  + lemmas `powerset_sigma_ring`, `g_sigma_ring_strace`, `setI_g_sigma_ring`,
+    `subset_strace`
 
 - in `lebesgue_measure.v`:
   + lemma `measurable_fun_ler`
@@ -74,6 +97,9 @@
 - in `Rstruct.v`:
   + lemma `IZRposE`
 
+- in `measure.v`:
+  + lemma `strace_sigma_ring`
+
 ### Changed
 
 - in `forms.v`:
@@ -86,6 +112,28 @@
 
 - in `measure.v`:
   + change the hypothesis of `measurable_fun_bool`
+  + mixin `AlgebraOfSets_isMeasurable` renamed to `hasMeasurableCountableUnion`
+    and made to inherit from `SemiRingOfSets`
+
+- in `measure.v`:
+  + rm hypo and variable in lemma `smallest_monotone_classE`
+    and rename to `smallest_lambda_system`
+  + rm hypo in lemma `monotone_class_g_salgebra` and renamed
+    to `g_salgebra_lambda_system`
+  + rm hypo in lemma `monotone_class_subset` and renamed to
+    `lambda_system_subset`
+  + notation `<<m _, _>>` changed to `<<l _, _>>`,
+    notation `<<m _>>` changed to `<<l _>>`
+
+- moved from `lebesgue_measure.v` to `measure.v`:
+  + definition `strace`
+  + lemma `sigma_algebra_strace`
+
+- in `sequences.v`:
+  + equality reversed in lemma `eq_bigcup_seqD`
+- in `sequences.v`:
+  + `eq_bigsetU_seqD` renamed to `nondecreasing_bigsetU_seqD`
+    and equality reversed
 
 ### Renamed
 
@@ -135,10 +183,23 @@
   + `num_lte_maxl` -> `num_gte_max`
   + `num_lte_minr` -> `num_lte_min`
   + `num_lte_minl` -> `num_gte_min`
+- in `measure.v`:
+  + `bigcap_measurable` -> `bigcap_measurableType`
 
 - in `lebesgue_integral.v`:
   + `integral_measure_add` -> `ge0_integral_measure_add`
   + `integral_pushforward` -> `ge0_integral_pushforward`
+- in `measure.v`:
+  + `monotone_class` -> `lambda_system`
+  + `monotone_class_g_salgebra` -> `g_sigma_algebra_lambda_system`
+  + `smallest_monotone_classE` -> `smallest_lambda_system`
+  + `dynkin_monotone` -> `dynkin_lambda_system`
+  + `dynkin_g_dynkin` -> `g_dynkin_dynkin`
+  + `salgebraType` -> `g_sigma_algebraType`
+  + `g_salgebra_measure_unique_trace` -> `g_sigma_algebra_measure_unique_trace`
+  + `g_salgebra_measure_unique_cover` -> `g_sigma_algebra_measure_unique_cover`
+  + `g_salgebra_measure_unique` -> `g_sigma_algebra_measure_unique`
+  + `setI_closed_gdynkin_salgebra` -> `setI_closed_g_dynkin_g_sigma_algebra`
 
 ### Generalized
 
@@ -165,6 +226,45 @@
 
 - in `probability.v`:
   + lemma `markov`
+- in `measure.v`:
+  + from `measurableType` to `sigmaRingType`
+    * lemmas `bigcup_measurable`, `bigcapT_measurable`
+	* definition `measurable_fun`
+	* lemmas `measurable_id`, `measurable_comp`, `eq_measurable_fun`, `measurable_cst`,
+	  `measurable_fun_bigcup`, `measurable_funU`, `measurable_funS`, `measurable_fun_if`
+	* lemmas `semi_sigma_additiveE`, `sigma_additive_is_additive`, `measure_sigma_additive`
+	* definitions `pushforward`, `dirac`
+	* lemmas `diracE`, `dirac0`, `diracT`, `finite_card_sum`, `finite_card_dirac`, `infinite_card_dirac`
+	* definitions `msum`, `measure_add`, `mscale`, `mseries`, `mrestr`
+	* lemmas `msum_mzero`, `measure_addE`
+	* definition `sfinite_measure`
+	* mixin `isSFinite`, structure `SFiniteMeasure`
+	* structure `FiniteMeasure`
+	* factory `Measure_isSFinite`
+	* lemma `negligible_bigcup`
+	* definition `ae_eq`
+	* lemmas `ae_eq0`, `ae_eq_comp`, `ae_eq_funeposneg`, `ae_eq_refl`, `ae_eq_sym`,
+	  `ae_eq_trans`, `ae_eq_sub`, `ae_eq_mul2r`, `ae_eq_mul2l`, `ae_eq_mul1l`,
+	  `ae_eq_abse`, `ae_eq_subset`
+  + from `measurableType` to `sigmaRingType` and from `realType` to `realFieldType`
+	* definition `mzero`
+  + from `realType` to `realFieldType`:
+    * lemma `sigma_finite_mzero`
+
+- in `lebesgue_integral.v`:
+  + from `measurableType` to `sigmaRingType`
+    * mixin `isMeasurableFun` 
+    * structure `SimpleFun`
+	* structure `NonNegSimpleFun`
+	* sections `fimfun_bin`, `mfun_pred`, `sfun_pred`, `simple_bounded`
+	* lemmas `nnfun_muleindic_ge0`, `mulemu_ge0`, `nnsfun_mulemu_ge0`
+	* section `sintegral_lemmas`
+	* lemma `eq_sintegral`
+	* section `sintegralrM`
+
+- in `lebesgue_measure.v`:
+  + from `measurableType` to `sigmaRingType`
+    * section `measurable_fun_measurable`
 
 ### Deprecated
 
@@ -190,6 +290,8 @@
 
 - in `reals.v`
   + lemma `inf_lower_bound` (use `inf_lb` instead)
+- in `lebesgue_measure.v`:
+  + lemmas `stracexx`, `strace_measurable`
 
 ### Infrastructure
 

classical/classical_sets.v

@@ -451,6 +451,10 @@ Notation "`] a , '+oo' [" :=
 Notation "`] -oo , '+oo' [" :=
   [set` Interval -oo%O +oo%O] : classical_set_scope.
 
+Lemma nat_nonempty : [set: nat] !=set0. Proof. by exists 1%N. Qed.
+
+#[global] Hint Resolve nat_nonempty : core.
+
 Lemma preimage_itv T d (rT : porderType d) (f : T -> rT) (i : interval rT) (x : T) :
   ((f @^-1` [set` i]) x) = (f x \in i).
 Proof. by rewrite inE. Qed.
@@ -1028,6 +1032,9 @@ Proof. by move=> *; rewrite setUC setUKD. Qed.
 Lemma setIDA A B C : A `&` (B `\` C) = (A `&` B) `\` C.
 Proof. by rewrite !setDE setIA. Qed.
 
+Lemma setIDAC A B C : (A `\` B) `&` C = A `&` (C `\` B).
+Proof. by rewrite setIC !setIDA setIC. Qed.
+
 Lemma setDD A B : A `\` (A `\` B) = A `&` B.
 Proof. by rewrite 2!setDE setCI setCK setIUr setICr set0U. Qed.
 
@@ -1043,6 +1050,15 @@ Proof. by rewrite !setDE setCI setIUr. Qed.
 Lemma setUIDK A B : (A `&` B) `|` A `\` B = A.
 Proof. by rewrite setUC -setDDr setDv setD0. Qed.
 
+Lemma setDUD A B C : (A `|` B) `\` C = A `\` C `|` B `\` C.
+Proof.
+apply/seteqP; split=> [x [[Ax|Bx] Cx]|x [[Ax]|[Bx] Cx]].
+- by left.
+- by right.
+- by split=> //; left.
+- by split=> //; right.
+Qed.
+
 Lemma setM0 T' (A : set T) : A `*` set0 = set0 :> set (T * T').
 Proof. by rewrite predeqE => -[t u]; split => // -[]. Qed.
 
@@ -1922,6 +1938,15 @@ End bigop_lemmas.
 Arguments bigcup_setD1 {T I} x.
 Arguments bigcap_setD1 {T I} x.
 
+Lemma setD_bigcup {T} (I : eqType) (F : I -> set T) (P : set I) (j : I) : P j ->
+  F j `\` \bigcup_(i in [set k | P k /\ k != j]) (F j `\` F i) =
+  \bigcap_(i in P) F i.
+Proof.
+move=> Pj; apply/seteqP; split => [t [Fjt UFt] i Pi|t UFt].
+  by have [->//|ij] := eqVneq i j; apply: contra_notP UFt => Fit; exists i.
+by split=> [|[k [Pk kj]] [Fjt]]; [|apply]; exact: UFt.
+Qed.
+
 Definition bigcup2 T (A B : set T) : nat -> set T :=
   fun i => if i == 0 then A else if i == 1 then B else set0.
 Arguments bigcup2 T A B n /.

theories/charge.v

@@ -1177,10 +1177,11 @@ rewrite is_max_approxRNE; apply: measurableI => /=.
   rewrite -[X in measurable X]setTI.
   by apply: emeasurable_fun_eq => //; [exact: measurable_max_approxRN_seq|
                                        exact: measurable_approxRN_seq].
-rewrite [T in measurable T](_ : _ = \bigcap_(k in `I_j) [set x | g_ k x < g_ j x])//.
-apply: bigcap_measurable => k _.
-rewrite -[X in measurable X]setTI; apply: emeasurable_fun_lt => //;
-exact: measurable_approxRN_seq.
+rewrite [T in measurable T](_ : _ =
+  \bigcap_(k in `I_j) [set x | g_ k x < g_ j x])//.
+apply: bigcap_measurableType => k _.
+by rewrite -[X in measurable X]setTI; apply: emeasurable_fun_lt => //;
+  exact: measurable_approxRN_seq.
 Qed.
 
 End approxRN_seq.
@@ -1881,7 +1882,7 @@ rewrite -(ae_eq_integral _ _ _ _ _
 - apply: emeasurable_funM => //; first exact: measurable_int mf.
   exact: measurable_funTS.
 rewrite [in LHS](funeposneg f).
-under eq_integral => x xE. rewrite muleBl; last 2 first.
+under [in LHS]eq_integral => x xE. rewrite muleBl; last 2 first.
   - exact: Radon_Nikodym_SigmaFinite.f_fin_num.
   - exact: add_def_funeposneg.
   over.

theories/kernel.v

@@ -457,7 +457,7 @@ have CXY : C `<=` XY.
   rewrite phiM.
   apply: emeasurable_funM => //; first exact/measurable_kernel/measurableI.
   by apply/EFin_measurable_fun; rewrite (_ : \1_ _ = mindic R mA).
-suff monoB : monotone_class setT XY by exact: monotone_class_subset.
+suff lsystemB : lambda_system setT XY by exact: lambda_system_subset.
 split => //; [exact: CXY| |exact: xsection_ndseq_closed].
 move=> A B BA [mA mphiA] [mB mphiB]; split; first exact: measurableD.
 suff : phi (A `\` B) = (fun x => phi A x - phi B x).