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Theorem List for Metamath Proof Explorer - 32201-32300   *Has distinct variable group(s)
TypeLabelDescription
Statement
 
Theoremmeasdivcst 32201 Division of a measure by a positive constant is a measure. (Contributed by Thierry Arnoux, 25-Dec-2016.) (Revised by Thierry Arnoux, 30-Jan-2017.)
((𝑀 ∈ (measures‘𝑆) ∧ 𝐴 ∈ ℝ+) → (𝑀f/c /𝑒 𝐴) ∈ (measures‘𝑆))
 
TheoremmeasdivcstALTV 32202* Alternate version of measdivcst 32201. (Contributed by Thierry Arnoux, 25-Dec-2016.) (New usage is discouraged.)
((𝑀 ∈ (measures‘𝑆) ∧ 𝐴 ∈ ℝ+) → (𝑥𝑆 ↦ ((𝑀𝑥) /𝑒 𝐴)) ∈ (measures‘𝑆))
 
20.3.17.7  The counting measure
 
Theoremcntmeas 32203 The Counting measure is a measure on any sigma-algebra. (Contributed by Thierry Arnoux, 25-Dec-2016.)
(𝑆 ran sigAlgebra → (♯ ↾ 𝑆) ∈ (measures‘𝑆))
 
Theorempwcntmeas 32204 The counting measure is a measure on any power set. (Contributed by Thierry Arnoux, 24-Jan-2017.)
(𝑂𝑉 → (♯ ↾ 𝒫 𝑂) ∈ (measures‘𝒫 𝑂))
 
Theoremcntnevol 32205 Counting and Lebesgue measures are different. (Contributed by Thierry Arnoux, 27-Jan-2017.)
(♯ ↾ 𝒫 𝑂) ≠ vol
 
20.3.17.8  The Lebesgue measure - misc additions
 
Theoremvoliune 32206 The Lebesgue measure function is countably additive. This formulation on the extended reals, allows for +∞ for the measure of any set in the sum. Cf. ovoliun 24678 and voliun 24727. (Contributed by Thierry Arnoux, 16-Oct-2017.)
((∀𝑛 ∈ ℕ 𝐴 ∈ dom vol ∧ Disj 𝑛 ∈ ℕ 𝐴) → (vol‘ 𝑛 ∈ ℕ 𝐴) = Σ*𝑛 ∈ ℕ(vol‘𝐴))
 
Theoremvolfiniune 32207* The Lebesgue measure function is countably additive. This theorem is to volfiniun 24720 what voliune 32206 is to voliun 24727. (Contributed by Thierry Arnoux, 16-Oct-2017.)
((𝐴 ∈ Fin ∧ ∀𝑛𝐴 𝐵 ∈ dom vol ∧ Disj 𝑛𝐴 𝐵) → (vol‘ 𝑛𝐴 𝐵) = Σ*𝑛𝐴(vol‘𝐵))
 
Theoremvolmeas 32208 The Lebesgue measure is a measure. (Contributed by Thierry Arnoux, 16-Oct-2017.)
vol ∈ (measures‘dom vol)
 
20.3.17.9  The Dirac delta measure
 
Syntaxcdde 32209 Extend class notation to include the Dirac delta measure.
class δ
 
Definitiondf-dde 32210 Define the Dirac delta measure. (Contributed by Thierry Arnoux, 14-Sep-2018.)
δ = (𝑎 ∈ 𝒫 ℝ ↦ if(0 ∈ 𝑎, 1, 0))
 
Theoremddeval1 32211 Value of the delta measure. (Contributed by Thierry Arnoux, 14-Sep-2018.)
((𝐴 ⊆ ℝ ∧ 0 ∈ 𝐴) → (δ‘𝐴) = 1)
 
Theoremddeval0 32212 Value of the delta measure. (Contributed by Thierry Arnoux, 14-Sep-2018.)
((𝐴 ⊆ ℝ ∧ ¬ 0 ∈ 𝐴) → (δ‘𝐴) = 0)
 
Theoremddemeas 32213 The Dirac delta measure is a measure. (Contributed by Thierry Arnoux, 14-Sep-2018.)
δ ∈ (measures‘𝒫 ℝ)
 
20.3.17.10  The 'almost everywhere' relation
 
Syntaxcae 32214 Extend class notation to include the 'almost everywhere' relation.
class a.e.
 
Syntaxcfae 32215 Extend class notation to include the 'almost everywhere' builder.
class ~ a.e.
 
Definitiondf-ae 32216* Define 'almost everywhere' with regard to a measure 𝑀. A property holds almost everywhere if the measure of the set where it does not hold has measure zero. (Contributed by Thierry Arnoux, 20-Oct-2017.)
a.e. = {⟨𝑎, 𝑚⟩ ∣ (𝑚‘( dom 𝑚𝑎)) = 0}
 
Theoremrelae 32217 'almost everywhere' is a relation. (Contributed by Thierry Arnoux, 20-Oct-2017.)
Rel a.e.
 
Theorembrae 32218 'almost everywhere' relation for a measure and a measurable set 𝐴. (Contributed by Thierry Arnoux, 20-Oct-2017.)
((𝑀 ran measures ∧ 𝐴 ∈ dom 𝑀) → (𝐴a.e.𝑀 ↔ (𝑀‘( dom 𝑀𝐴)) = 0))
 
Theorembraew 32219* 'almost everywhere' relation for a measure 𝑀 and a property 𝜑 (Contributed by Thierry Arnoux, 20-Oct-2017.)
dom 𝑀 = 𝑂       (𝑀 ran measures → ({𝑥𝑂𝜑}a.e.𝑀 ↔ (𝑀‘{𝑥𝑂 ∣ ¬ 𝜑}) = 0))
 
Theoremtruae 32220* A truth holds almost everywhere. (Contributed by Thierry Arnoux, 20-Oct-2017.)
dom 𝑀 = 𝑂    &   (𝜑𝑀 ran measures)    &   (𝜑𝜓)       (𝜑 → {𝑥𝑂𝜓}a.e.𝑀)
 
Theoremaean 32221* A conjunction holds almost everywhere if and only if both its terms do. (Contributed by Thierry Arnoux, 20-Oct-2017.)
dom 𝑀 = 𝑂       ((𝑀 ran measures ∧ {𝑥𝑂 ∣ ¬ 𝜑} ∈ dom 𝑀 ∧ {𝑥𝑂 ∣ ¬ 𝜓} ∈ dom 𝑀) → ({𝑥𝑂 ∣ (𝜑𝜓)}a.e.𝑀 ↔ ({𝑥𝑂𝜑}a.e.𝑀 ∧ {𝑥𝑂𝜓}a.e.𝑀)))
 
Definitiondf-fae 32222* Define a builder for an 'almost everywhere' relation between functions, from relations between function values. In this definition, the range of 𝑓 and 𝑔 is enforced in order to ensure the resulting relation is a set. (Contributed by Thierry Arnoux, 22-Oct-2017.)
~ a.e. = (𝑟 ∈ V, 𝑚 ran measures ↦ {⟨𝑓, 𝑔⟩ ∣ ((𝑓 ∈ (dom 𝑟m dom 𝑚) ∧ 𝑔 ∈ (dom 𝑟m dom 𝑚)) ∧ {𝑥 dom 𝑚 ∣ (𝑓𝑥)𝑟(𝑔𝑥)}a.e.𝑚)})
 
Theoremfaeval 32223* Value of the 'almost everywhere' relation for a given relation and measure. (Contributed by Thierry Arnoux, 22-Oct-2017.)
((𝑅 ∈ V ∧ 𝑀 ran measures) → (𝑅~ a.e.𝑀) = {⟨𝑓, 𝑔⟩ ∣ ((𝑓 ∈ (dom 𝑅m dom 𝑀) ∧ 𝑔 ∈ (dom 𝑅m dom 𝑀)) ∧ {𝑥 dom 𝑀 ∣ (𝑓𝑥)𝑅(𝑔𝑥)}a.e.𝑀)})
 
Theoremrelfae 32224 The 'almost everywhere' builder for functions produces relations. (Contributed by Thierry Arnoux, 22-Oct-2017.)
((𝑅 ∈ V ∧ 𝑀 ran measures) → Rel (𝑅~ a.e.𝑀))
 
Theorembrfae 32225* 'almost everywhere' relation for two functions 𝐹 and 𝐺 with regard to the measure 𝑀. (Contributed by Thierry Arnoux, 22-Oct-2017.)
dom 𝑅 = 𝐷    &   (𝜑𝑅 ∈ V)    &   (𝜑𝑀 ran measures)    &   (𝜑𝐹 ∈ (𝐷m dom 𝑀))    &   (𝜑𝐺 ∈ (𝐷m dom 𝑀))       (𝜑 → (𝐹(𝑅~ a.e.𝑀)𝐺 ↔ {𝑥 dom 𝑀 ∣ (𝐹𝑥)𝑅(𝐺𝑥)}a.e.𝑀))
 
20.3.17.11  Measurable functions
 
Syntaxcmbfm 32226 Extend class notation with the measurable functions builder.
class MblFnM
 
Definitiondf-mbfm 32227* Define the measurable function builder, which generates the set of measurable functions from a measurable space to another one. Here, the measurable spaces are given using their sigma-algebras 𝑠 and 𝑡, and the spaces themselves are recovered by 𝑠 and 𝑡.

Note the similarities between the definition of measurable functions in measure theory, and of continuous functions in topology.

This is the definition for the generic measure theory. For the specific case of functions from to , see df-mbf 24792. (Contributed by Thierry Arnoux, 23-Jan-2017.)

MblFnM = (𝑠 ran sigAlgebra, 𝑡 ran sigAlgebra ↦ {𝑓 ∈ ( 𝑡m 𝑠) ∣ ∀𝑥𝑡 (𝑓𝑥) ∈ 𝑠})
 
Theoremismbfm 32228* The predicate "𝐹 is a measurable function from the measurable space 𝑆 to the measurable space 𝑇". Cf. ismbf 24801. (Contributed by Thierry Arnoux, 23-Jan-2017.)
(𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)       (𝜑 → (𝐹 ∈ (𝑆MblFnM𝑇) ↔ (𝐹 ∈ ( 𝑇m 𝑆) ∧ ∀𝑥𝑇 (𝐹𝑥) ∈ 𝑆)))
 
Theoremelunirnmbfm 32229* The property of being a measurable function. (Contributed by Thierry Arnoux, 23-Jan-2017.)
(𝐹 ran MblFnM ↔ ∃𝑠 ran sigAlgebra∃𝑡 ran sigAlgebra(𝐹 ∈ ( 𝑡m 𝑠) ∧ ∀𝑥𝑡 (𝐹𝑥) ∈ 𝑠))
 
Theoremmbfmfun 32230 A measurable function is a function. (Contributed by Thierry Arnoux, 24-Jan-2017.)
(𝜑𝐹 ran MblFnM)       (𝜑 → Fun 𝐹)
 
Theoremmbfmf 32231 A measurable function as a function with domain and codomain. (Contributed by Thierry Arnoux, 25-Jan-2017.)
(𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)    &   (𝜑𝐹 ∈ (𝑆MblFnM𝑇))       (𝜑𝐹: 𝑆 𝑇)
 
Theoremisanmbfm 32232 The predicate to be a measurable function. (Contributed by Thierry Arnoux, 30-Jan-2017.)
(𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)    &   (𝜑𝐹 ∈ (𝑆MblFnM𝑇))       (𝜑𝐹 ran MblFnM)
 
Theoremmbfmcnvima 32233 The preimage by a measurable function is a measurable set. (Contributed by Thierry Arnoux, 23-Jan-2017.)
(𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)    &   (𝜑𝐹 ∈ (𝑆MblFnM𝑇))    &   (𝜑𝐴𝑇)       (𝜑 → (𝐹𝐴) ∈ 𝑆)
 
Theoremmbfmbfm 32234 A measurable function to a Borel Set is measurable. (Contributed by Thierry Arnoux, 24-Jan-2017.)
(𝜑𝑀 ran measures)    &   (𝜑𝐽 ∈ Top)    &   (𝜑𝐹 ∈ (dom 𝑀MblFnM(sigaGen‘𝐽)))       (𝜑𝐹 ran MblFnM)
 
Theoremmbfmcst 32235* A constant function is measurable. Cf. mbfconst 24806. (Contributed by Thierry Arnoux, 26-Jan-2017.)
(𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)    &   (𝜑𝐹 = (𝑥 𝑆𝐴))    &   (𝜑𝐴 𝑇)       (𝜑𝐹 ∈ (𝑆MblFnM𝑇))
 
Theorem1stmbfm 32236 The first projection map is measurable with regard to the product sigma-algebra. (Contributed by Thierry Arnoux, 3-Jun-2017.)
(𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)       (𝜑 → (1st ↾ ( 𝑆 × 𝑇)) ∈ ((𝑆 ×s 𝑇)MblFnM𝑆))
 
Theorem2ndmbfm 32237 The second projection map is measurable with regard to the product sigma-algebra. (Contributed by Thierry Arnoux, 3-Jun-2017.)
(𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)       (𝜑 → (2nd ↾ ( 𝑆 × 𝑇)) ∈ ((𝑆 ×s 𝑇)MblFnM𝑇))
 
Theoremimambfm 32238* If the sigma-algebra in the range of a given function is generated by a collection of basic sets 𝐾, then to check the measurability of that function, we need only consider inverse images of basic sets 𝑎. (Contributed by Thierry Arnoux, 4-Jun-2017.)
(𝜑𝐾 ∈ V)    &   (𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 = (sigaGen‘𝐾))       (𝜑 → (𝐹 ∈ (𝑆MblFnM𝑇) ↔ (𝐹: 𝑆 𝑇 ∧ ∀𝑎𝐾 (𝐹𝑎) ∈ 𝑆)))
 
Theoremcnmbfm 32239 A continuous function is measurable with respect to the Borel Algebra of its domain and range. (Contributed by Thierry Arnoux, 3-Jun-2017.)
(𝜑𝐹 ∈ (𝐽 Cn 𝐾))    &   (𝜑𝑆 = (sigaGen‘𝐽))    &   (𝜑𝑇 = (sigaGen‘𝐾))       (𝜑𝐹 ∈ (𝑆MblFnM𝑇))
 
Theoremmbfmco 32240 The composition of two measurable functions is measurable. See cnmpt11 22823. (Contributed by Thierry Arnoux, 4-Jun-2017.)
(𝜑𝑅 ran sigAlgebra)    &   (𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)    &   (𝜑𝐹 ∈ (𝑅MblFnM𝑆))    &   (𝜑𝐺 ∈ (𝑆MblFnM𝑇))       (𝜑 → (𝐺𝐹) ∈ (𝑅MblFnM𝑇))
 
Theoremmbfmco2 32241* The pair building of two measurable functions is measurable. ( cf. cnmpt1t 22825). (Contributed by Thierry Arnoux, 6-Jun-2017.)
(𝜑𝑅 ran sigAlgebra)    &   (𝜑𝑆 ran sigAlgebra)    &   (𝜑𝑇 ran sigAlgebra)    &   (𝜑𝐹 ∈ (𝑅MblFnM𝑆))    &   (𝜑𝐺 ∈ (𝑅MblFnM𝑇))    &   𝐻 = (𝑥 𝑅 ↦ ⟨(𝐹𝑥), (𝐺𝑥)⟩)       (𝜑𝐻 ∈ (𝑅MblFnM(𝑆 ×s 𝑇)))
 
Theoremmbfmvolf 32242 Measurable functions with respect to the Lebesgue measure are real-valued functions on the real numbers. (Contributed by Thierry Arnoux, 27-Mar-2017.)
(𝐹 ∈ (dom volMblFnM𝔅) → 𝐹:ℝ⟶ℝ)
 
Theoremelmbfmvol2 32243 Measurable functions with respect to the Lebesgue measure. We only have the inclusion, since MblFn includes complex-valued functions. (Contributed by Thierry Arnoux, 26-Jan-2017.)
(𝐹 ∈ (dom volMblFnM𝔅) → 𝐹 ∈ MblFn)
 
Theoremmbfmcnt 32244 All functions are measurable with respect to the counting measure. (Contributed by Thierry Arnoux, 24-Jan-2017.)
(𝑂𝑉 → (𝒫 𝑂MblFnM𝔅) = (ℝ ↑m 𝑂))
 
20.3.17.12  Borel Algebra on ` ( RR X. RR ) `
 
Theorembr2base 32245* The base set for the generator of the Borel sigma-algebra on (ℝ × ℝ) is indeed (ℝ × ℝ). (Contributed by Thierry Arnoux, 22-Sep-2017.)
ran (𝑥 ∈ 𝔅, 𝑦 ∈ 𝔅 ↦ (𝑥 × 𝑦)) = (ℝ × ℝ)
 
Theoremdya2ub 32246 An upper bound for a dyadic number. (Contributed by Thierry Arnoux, 19-Sep-2017.)
(𝑅 ∈ ℝ+ → (1 / (2↑(⌊‘(1 − (2 logb 𝑅))))) < 𝑅)
 
Theoremsxbrsigalem0 32247* The closed half-spaces of (ℝ × ℝ) cover (ℝ × ℝ). (Contributed by Thierry Arnoux, 11-Oct-2017.)
(ran (𝑒 ∈ ℝ ↦ ((𝑒[,)+∞) × ℝ)) ∪ ran (𝑓 ∈ ℝ ↦ (ℝ × (𝑓[,)+∞)))) = (ℝ × ℝ)
 
Theoremsxbrsigalem3 32248* The sigma-algebra generated by the closed half-spaces of (ℝ × ℝ) is a subset of the sigma-algebra generated by the closed sets of (ℝ × ℝ). (Contributed by Thierry Arnoux, 11-Oct-2017.)
𝐽 = (topGen‘ran (,))       (sigaGen‘(ran (𝑒 ∈ ℝ ↦ ((𝑒[,)+∞) × ℝ)) ∪ ran (𝑓 ∈ ℝ ↦ (ℝ × (𝑓[,)+∞))))) ⊆ (sigaGen‘(Clsd‘(𝐽 ×t 𝐽)))
 
Theoremdya2iocival 32249* The function 𝐼 returns closed-below open-above dyadic rational intervals covering the real line. This is the same construction as in dyadmbl 24773. (Contributed by Thierry Arnoux, 24-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))       ((𝑁 ∈ ℤ ∧ 𝑋 ∈ ℤ) → (𝑋𝐼𝑁) = ((𝑋 / (2↑𝑁))[,)((𝑋 + 1) / (2↑𝑁))))
 
Theoremdya2iocress 32250* Dyadic intervals are subsets of . (Contributed by Thierry Arnoux, 18-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))       ((𝑁 ∈ ℤ ∧ 𝑋 ∈ ℤ) → (𝑋𝐼𝑁) ⊆ ℝ)
 
Theoremdya2iocbrsiga 32251* Dyadic intervals are Borel sets of . (Contributed by Thierry Arnoux, 22-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))       ((𝑁 ∈ ℤ ∧ 𝑋 ∈ ℤ) → (𝑋𝐼𝑁) ∈ 𝔅)
 
Theoremdya2icobrsiga 32252* Dyadic intervals are Borel sets of . (Contributed by Thierry Arnoux, 22-Sep-2017.) (Revised by Thierry Arnoux, 13-Oct-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))       ran 𝐼 ⊆ 𝔅
 
Theoremdya2icoseg 32253* For any point and any closed-below, open-above interval of centered on that point, there is a closed-below open-above dyadic rational interval which contains that point and is included in the original interval. (Contributed by Thierry Arnoux, 19-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑁 = (⌊‘(1 − (2 logb 𝐷)))       ((𝑋 ∈ ℝ ∧ 𝐷 ∈ ℝ+) → ∃𝑏 ∈ ran 𝐼(𝑋𝑏𝑏 ⊆ ((𝑋𝐷)(,)(𝑋 + 𝐷))))
 
Theoremdya2icoseg2 32254* For any point and any open interval of containing that point, there is a closed-below open-above dyadic rational interval which contains that point and is included in the original interval. (Contributed by Thierry Arnoux, 12-Oct-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))       ((𝑋 ∈ ℝ ∧ 𝐸 ∈ ran (,) ∧ 𝑋𝐸) → ∃𝑏 ∈ ran 𝐼(𝑋𝑏𝑏𝐸))
 
Theoremdya2iocrfn 32255* The function returning dyadic square covering for a given size has domain (ran 𝐼 × ran 𝐼). (Contributed by Thierry Arnoux, 19-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))       𝑅 Fn (ran 𝐼 × ran 𝐼)
 
Theoremdya2iocct 32256* The dyadic rectangle set is countable. (Contributed by Thierry Arnoux, 18-Sep-2017.) (Revised by Thierry Arnoux, 11-Oct-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))       ran 𝑅 ≼ ω
 
Theoremdya2iocnrect 32257* For any point of an open rectangle in (ℝ × ℝ), there is a closed-below open-above dyadic rational square which contains that point and is included in the rectangle. (Contributed by Thierry Arnoux, 12-Oct-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))    &   𝐵 = ran (𝑒 ∈ ran (,), 𝑓 ∈ ran (,) ↦ (𝑒 × 𝑓))       ((𝑋 ∈ (ℝ × ℝ) ∧ 𝐴𝐵𝑋𝐴) → ∃𝑏 ∈ ran 𝑅(𝑋𝑏𝑏𝐴))
 
Theoremdya2iocnei 32258* For any point of an open set of the usual topology on (ℝ × ℝ) there is a closed-below open-above dyadic rational square which contains that point and is entirely in the open set. (Contributed by Thierry Arnoux, 21-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))       ((𝐴 ∈ (𝐽 ×t 𝐽) ∧ 𝑋𝐴) → ∃𝑏 ∈ ran 𝑅(𝑋𝑏𝑏𝐴))
 
Theoremdya2iocuni 32259* Every open set of (ℝ × ℝ) is a union of closed-below open-above dyadic rational rectangular subsets of (ℝ × ℝ). This union must be a countable union by dya2iocct 32256. (Contributed by Thierry Arnoux, 18-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))       (𝐴 ∈ (𝐽 ×t 𝐽) → ∃𝑐 ∈ 𝒫 ran 𝑅 𝑐 = 𝐴)
 
Theoremdya2iocucvr 32260* The dyadic rectangular set collection covers (ℝ × ℝ). (Contributed by Thierry Arnoux, 18-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))        ran 𝑅 = (ℝ × ℝ)
 
Theoremsxbrsigalem1 32261* The Borel algebra on (ℝ × ℝ) is a subset of the sigma-algebra generated by the dyadic closed-below, open-above rectangular subsets of (ℝ × ℝ). This is a step of the proof of Proposition 1.1.5 of [Cohn] p. 4. (Contributed by Thierry Arnoux, 17-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))       (sigaGen‘(𝐽 ×t 𝐽)) ⊆ (sigaGen‘ran 𝑅)
 
Theoremsxbrsigalem2 32262* The sigma-algebra generated by the dyadic closed-below, open-above rectangular subsets of (ℝ × ℝ) is a subset of the sigma-algebra generated by the closed half-spaces of (ℝ × ℝ). The proof goes by noting the fact that the dyadic rectangles are intersections of a 'vertical band' and an 'horizontal band', which themselves are differences of closed half-spaces. (Contributed by Thierry Arnoux, 17-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))       (sigaGen‘ran 𝑅) ⊆ (sigaGen‘(ran (𝑒 ∈ ℝ ↦ ((𝑒[,)+∞) × ℝ)) ∪ ran (𝑓 ∈ ℝ ↦ (ℝ × (𝑓[,)+∞)))))
 
Theoremsxbrsigalem4 32263* The Borel algebra on (ℝ × ℝ) is generated by the dyadic closed-below, open-above rectangular subsets of (ℝ × ℝ). Proposition 1.1.5 of [Cohn] p. 4 . Note that the interval used in this formalization are closed-below, open-above instead of open-below, closed-above in the proof as they are ultimately generated by the floor function. (Contributed by Thierry Arnoux, 21-Sep-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))       (sigaGen‘(𝐽 ×t 𝐽)) = (sigaGen‘ran 𝑅)
 
Theoremsxbrsigalem5 32264* First direction for sxbrsiga 32266. (Contributed by Thierry Arnoux, 22-Sep-2017.) (Revised by Thierry Arnoux, 11-Oct-2017.)
𝐽 = (topGen‘ran (,))    &   𝐼 = (𝑥 ∈ ℤ, 𝑛 ∈ ℤ ↦ ((𝑥 / (2↑𝑛))[,)((𝑥 + 1) / (2↑𝑛))))    &   𝑅 = (𝑢 ∈ ran 𝐼, 𝑣 ∈ ran 𝐼 ↦ (𝑢 × 𝑣))       (sigaGen‘(𝐽 ×t 𝐽)) ⊆ (𝔅 ×s 𝔅)
 
Theoremsxbrsigalem6 32265 First direction for sxbrsiga 32266, same as sxbrsigalem6, dealing with the antecedents. (Contributed by Thierry Arnoux, 10-Oct-2017.)
𝐽 = (topGen‘ran (,))       (sigaGen‘(𝐽 ×t 𝐽)) ⊆ (𝔅 ×s 𝔅)
 
Theoremsxbrsiga 32266 The product sigma-algebra (𝔅 ×s 𝔅) is the Borel algebra on (ℝ × ℝ) See example 5.1.1 of [Cohn] p. 143 . (Contributed by Thierry Arnoux, 10-Oct-2017.)
𝐽 = (topGen‘ran (,))       (𝔅 ×s 𝔅) = (sigaGen‘(𝐽 ×t 𝐽))
 
20.3.17.13  Caratheodory's extension theorem

In this section, we define a function toOMeas which constructs an outer measure, from a pre-measure 𝑅. An explicit generic definition of an outer measure is not given. It consists of the three following statements: - the outer measure of an empty set is zero (oms0 32273) - it is monotone (omsmon 32274) - it is countably sub-additive (omssubadd 32276) See Definition 1.11.1 of [Bogachev] p. 41.

 
Syntaxcoms 32267 Class declaration for the outer measure construction function.
class toOMeas
 
Definitiondf-oms 32268* Define a function constructing an outer measure. See omsval 32269 for its value. Definition 1.5 of [Bogachev] p. 16. (Contributed by Thierry Arnoux, 15-Sep-2019.) (Revised by AV, 4-Oct-2020.)
toOMeas = (𝑟 ∈ V ↦ (𝑎 ∈ 𝒫 dom 𝑟 ↦ inf(ran (𝑥 ∈ {𝑧 ∈ 𝒫 dom 𝑟 ∣ (𝑎 𝑧𝑧 ≼ ω)} ↦ Σ*𝑦𝑥(𝑟𝑦)), (0[,]+∞), < )))
 
Theoremomsval 32269* Value of the function mapping a content function to the corresponding outer measure. (Contributed by Thierry Arnoux, 15-Sep-2019.) (Revised by AV, 4-Oct-2020.)
(𝑅 ∈ V → (toOMeas‘𝑅) = (𝑎 ∈ 𝒫 dom 𝑅 ↦ inf(ran (𝑥 ∈ {𝑧 ∈ 𝒫 dom 𝑅 ∣ (𝑎 𝑧𝑧 ≼ ω)} ↦ Σ*𝑦𝑥(𝑅𝑦)), (0[,]+∞), < )))
 
Theoremomsfval 32270* Value of the outer measure evaluated for a given set 𝐴. (Contributed by Thierry Arnoux, 15-Sep-2019.) (Revised by AV, 4-Oct-2020.)
((𝑄𝑉𝑅:𝑄⟶(0[,]+∞) ∧ 𝐴 𝑄) → ((toOMeas‘𝑅)‘𝐴) = inf(ran (𝑥 ∈ {𝑧 ∈ 𝒫 dom 𝑅 ∣ (𝐴 𝑧𝑧 ≼ ω)} ↦ Σ*𝑦𝑥(𝑅𝑦)), (0[,]+∞), < ))
 
Theoremomscl 32271* A closure lemma for the constructed outer measure. (Contributed by Thierry Arnoux, 17-Sep-2019.)
((𝑄𝑉𝑅:𝑄⟶(0[,]+∞) ∧ 𝐴 ∈ 𝒫 dom 𝑅) → ran (𝑥 ∈ {𝑧 ∈ 𝒫 dom 𝑅 ∣ (𝐴 𝑧𝑧 ≼ ω)} ↦ Σ*𝑦𝑥(𝑅𝑦)) ⊆ (0[,]+∞))
 
Theoremomsf 32272 A constructed outer measure is a function. (Contributed by Thierry Arnoux, 17-Sep-2019.) (Revised by AV, 4-Oct-2020.)
((𝑄𝑉𝑅:𝑄⟶(0[,]+∞)) → (toOMeas‘𝑅):𝒫 dom 𝑅⟶(0[,]+∞))
 
Theoremoms0 32273 A constructed outer measure evaluates to zero for the empty set. (Contributed by Thierry Arnoux, 15-Sep-2019.) (Revised by AV, 4-Oct-2020.)
𝑀 = (toOMeas‘𝑅)    &   (𝜑𝑄𝑉)    &   (𝜑𝑅:𝑄⟶(0[,]+∞))    &   (𝜑 → ∅ ∈ dom 𝑅)    &   (𝜑 → (𝑅‘∅) = 0)       (𝜑 → (𝑀‘∅) = 0)
 
Theoremomsmon 32274 A constructed outer measure is monotone. Note in Example 1.5.2 of [Bogachev] p. 17. (Contributed by Thierry Arnoux, 15-Sep-2019.) (Revised by AV, 4-Oct-2020.)
𝑀 = (toOMeas‘𝑅)    &   (𝜑𝑄𝑉)    &   (𝜑𝑅:𝑄⟶(0[,]+∞))    &   (𝜑𝐴𝐵)    &   (𝜑𝐵 𝑄)       (𝜑 → (𝑀𝐴) ≤ (𝑀𝐵))
 
Theoremomssubaddlem 32275* For any small margin 𝐸, we can find a covering approaching the outer measure of a set 𝐴 by that margin. (Contributed by Thierry Arnoux, 18-Sep-2019.) (Revised by AV, 4-Oct-2020.)
𝑀 = (toOMeas‘𝑅)    &   (𝜑𝑄𝑉)    &   (𝜑𝑅:𝑄⟶(0[,]+∞))    &   (𝜑𝐴 𝑄)    &   (𝜑 → (𝑀𝐴) ∈ ℝ)    &   (𝜑𝐸 ∈ ℝ+)       (𝜑 → ∃𝑥 ∈ {𝑧 ∈ 𝒫 dom 𝑅 ∣ (𝐴 𝑧𝑧 ≼ ω)}Σ*𝑤𝑥(𝑅𝑤) < ((𝑀𝐴) + 𝐸))
 
Theoremomssubadd 32276* A constructed outer measure is countably sub-additive. Lemma 1.5.4 of [Bogachev] p. 17. (Contributed by Thierry Arnoux, 21-Sep-2019.) (Revised by AV, 4-Oct-2020.)
𝑀 = (toOMeas‘𝑅)    &   (𝜑𝑄𝑉)    &   (𝜑𝑅:𝑄⟶(0[,]+∞))    &   ((𝜑𝑦𝑋) → 𝐴 𝑄)    &   (𝜑𝑋 ≼ ω)       (𝜑 → (𝑀 𝑦𝑋 𝐴) ≤ Σ*𝑦𝑋(𝑀𝐴))
 
Syntaxccarsg 32277 Class declaration for the Caratheodory sigma-Algebra construction.
class toCaraSiga
 
Definitiondf-carsg 32278* Define a function constructing Caratheodory measurable sets for a given outer measure. See carsgval 32279 for its value. Definition 1.11.2 of [Bogachev] p. 41. (Contributed by Thierry Arnoux, 17-May-2020.)
toCaraSiga = (𝑚 ∈ V ↦ {𝑎 ∈ 𝒫 dom 𝑚 ∣ ∀𝑒 ∈ 𝒫 dom 𝑚((𝑚‘(𝑒𝑎)) +𝑒 (𝑚‘(𝑒𝑎))) = (𝑚𝑒)})
 
Theoremcarsgval 32279* Value of the Caratheodory sigma-Algebra construction function. (Contributed by Thierry Arnoux, 17-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))       (𝜑 → (toCaraSiga‘𝑀) = {𝑎 ∈ 𝒫 𝑂 ∣ ∀𝑒 ∈ 𝒫 𝑂((𝑀‘(𝑒𝑎)) +𝑒 (𝑀‘(𝑒𝑎))) = (𝑀𝑒)})
 
Theoremcarsgcl 32280 Closure of the Caratheodory measurable sets. (Contributed by Thierry Arnoux, 17-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))       (𝜑 → (toCaraSiga‘𝑀) ⊆ 𝒫 𝑂)
 
Theoremelcarsg 32281* Property of being a Caratheodory measurable set. (Contributed by Thierry Arnoux, 17-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))       (𝜑 → (𝐴 ∈ (toCaraSiga‘𝑀) ↔ (𝐴𝑂 ∧ ∀𝑒 ∈ 𝒫 𝑂((𝑀‘(𝑒𝐴)) +𝑒 (𝑀‘(𝑒𝐴))) = (𝑀𝑒))))
 
Theorembaselcarsg 32282 The universe set, 𝑂, is Caratheodory measurable. (Contributed by Thierry Arnoux, 17-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)       (𝜑𝑂 ∈ (toCaraSiga‘𝑀))
 
Theorem0elcarsg 32283 The empty set is Caratheodory measurable. (Contributed by Thierry Arnoux, 30-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)       (𝜑 → ∅ ∈ (toCaraSiga‘𝑀))
 
Theoremcarsguni 32284 The union of all Caratheodory measurable sets is the universe. (Contributed by Thierry Arnoux, 22-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)       (𝜑 (toCaraSiga‘𝑀) = 𝑂)
 
Theoremelcarsgss 32285 Caratheodory measurable sets are subsets of the universe. (Contributed by Thierry Arnoux, 21-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑𝐴 ∈ (toCaraSiga‘𝑀))       (𝜑𝐴𝑂)
 
Theoremdifelcarsg 32286 The Caratheodory measurable sets are closed under complement. (Contributed by Thierry Arnoux, 17-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑𝐴 ∈ (toCaraSiga‘𝑀))       (𝜑 → (𝑂𝐴) ∈ (toCaraSiga‘𝑀))
 
Theoreminelcarsg 32287* The Caratheodory measurable sets are closed under intersection. (Contributed by Thierry Arnoux, 18-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑𝐴 ∈ (toCaraSiga‘𝑀))    &   ((𝜑𝑎 ∈ 𝒫 𝑂𝑏 ∈ 𝒫 𝑂) → (𝑀‘(𝑎𝑏)) ≤ ((𝑀𝑎) +𝑒 (𝑀𝑏)))    &   (𝜑𝐵 ∈ (toCaraSiga‘𝑀))       (𝜑 → (𝐴𝐵) ∈ (toCaraSiga‘𝑀))
 
Theoremunelcarsg 32288* The Caratheodory-measurable sets are closed under pairwise unions. (Contributed by Thierry Arnoux, 21-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑𝐴 ∈ (toCaraSiga‘𝑀))    &   ((𝜑𝑎 ∈ 𝒫 𝑂𝑏 ∈ 𝒫 𝑂) → (𝑀‘(𝑎𝑏)) ≤ ((𝑀𝑎) +𝑒 (𝑀𝑏)))    &   (𝜑𝐵 ∈ (toCaraSiga‘𝑀))       (𝜑 → (𝐴𝐵) ∈ (toCaraSiga‘𝑀))
 
Theoremdifelcarsg2 32289* The Caratheodory-measurable sets are closed under class difference. (Contributed by Thierry Arnoux, 30-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑𝐴 ∈ (toCaraSiga‘𝑀))    &   ((𝜑𝑎 ∈ 𝒫 𝑂𝑏 ∈ 𝒫 𝑂) → (𝑀‘(𝑎𝑏)) ≤ ((𝑀𝑎) +𝑒 (𝑀𝑏)))    &   (𝜑𝐵 ∈ (toCaraSiga‘𝑀))       (𝜑 → (𝐴𝐵) ∈ (toCaraSiga‘𝑀))
 
Theoremcarsgmon 32290* Utility lemma: Apply monotony. (Contributed by Thierry Arnoux, 29-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑𝐴𝐵)    &   (𝜑𝐵 ∈ 𝒫 𝑂)    &   ((𝜑𝑥𝑦𝑦 ∈ 𝒫 𝑂) → (𝑀𝑥) ≤ (𝑀𝑦))       (𝜑 → (𝑀𝐴) ≤ (𝑀𝐵))
 
Theoremcarsgsigalem 32291* Lemma for the following theorems. (Contributed by Thierry Arnoux, 23-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)    &   ((𝜑𝑥 ≼ ω ∧ 𝑥 ⊆ 𝒫 𝑂) → (𝑀 𝑥) ≤ Σ*𝑦𝑥(𝑀𝑦))       ((𝜑𝑒 ∈ 𝒫 𝑂𝑓 ∈ 𝒫 𝑂) → (𝑀‘(𝑒𝑓)) ≤ ((𝑀𝑒) +𝑒 (𝑀𝑓)))
 
Theoremfiunelcarsg 32292* The Caratheodory measurable sets are closed under finite union. (Contributed by Thierry Arnoux, 23-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)    &   ((𝜑𝑥 ≼ ω ∧ 𝑥 ⊆ 𝒫 𝑂) → (𝑀 𝑥) ≤ Σ*𝑦𝑥(𝑀𝑦))    &   (𝜑𝐴 ∈ Fin)    &   (𝜑𝐴 ⊆ (toCaraSiga‘𝑀))       (𝜑 𝐴 ∈ (toCaraSiga‘𝑀))
 
Theoremcarsgclctunlem1 32293* Lemma for carsgclctun 32297. (Contributed by Thierry Arnoux, 23-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)    &   ((𝜑𝑥 ≼ ω ∧ 𝑥 ⊆ 𝒫 𝑂) → (𝑀 𝑥) ≤ Σ*𝑦𝑥(𝑀𝑦))    &   (𝜑𝐴 ∈ Fin)    &   (𝜑𝐴 ⊆ (toCaraSiga‘𝑀))    &   (𝜑Disj 𝑦𝐴 𝑦)    &   (𝜑𝐸 ∈ 𝒫 𝑂)       (𝜑 → (𝑀‘(𝐸 𝐴)) = Σ*𝑦𝐴(𝑀‘(𝐸𝑦)))
 
Theoremcarsggect 32294* The outer measure is countably superadditive on Caratheodory measurable sets. (Contributed by Thierry Arnoux, 31-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)    &   ((𝜑𝑥 ≼ ω ∧ 𝑥 ⊆ 𝒫 𝑂) → (𝑀 𝑥) ≤ Σ*𝑦𝑥(𝑀𝑦))    &   (𝜑 → ¬ ∅ ∈ 𝐴)    &   (𝜑𝐴 ≼ ω)    &   (𝜑𝐴 ⊆ (toCaraSiga‘𝑀))    &   (𝜑Disj 𝑦𝐴 𝑦)    &   ((𝜑𝑥𝑦𝑦 ∈ 𝒫 𝑂) → (𝑀𝑥) ≤ (𝑀𝑦))       (𝜑 → Σ*𝑧𝐴(𝑀𝑧) ≤ (𝑀 𝐴))
 
Theoremcarsgclctunlem2 32295* Lemma for carsgclctun 32297. (Contributed by Thierry Arnoux, 25-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)    &   ((𝜑𝑥 ≼ ω ∧ 𝑥 ⊆ 𝒫 𝑂) → (𝑀 𝑥) ≤ Σ*𝑦𝑥(𝑀𝑦))    &   ((𝜑𝑥𝑦𝑦 ∈ 𝒫 𝑂) → (𝑀𝑥) ≤ (𝑀𝑦))    &   (𝜑Disj 𝑘 ∈ ℕ 𝐴)    &   ((𝜑𝑘 ∈ ℕ) → 𝐴 ∈ (toCaraSiga‘𝑀))    &   (𝜑𝐸 ∈ 𝒫 𝑂)    &   (𝜑 → (𝑀𝐸) ≠ +∞)       (𝜑 → ((𝑀‘(𝐸 𝑘 ∈ ℕ 𝐴)) +𝑒 (𝑀‘(𝐸 𝑘 ∈ ℕ 𝐴))) ≤ (𝑀𝐸))
 
Theoremcarsgclctunlem3 32296* Lemma for carsgclctun 32297. (Contributed by Thierry Arnoux, 24-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)    &   ((𝜑𝑥 ≼ ω ∧ 𝑥 ⊆ 𝒫 𝑂) → (𝑀 𝑥) ≤ Σ*𝑦𝑥(𝑀𝑦))    &   ((𝜑𝑥𝑦𝑦 ∈ 𝒫 𝑂) → (𝑀𝑥) ≤ (𝑀𝑦))    &   (𝜑𝐴 ≼ ω)    &   (𝜑𝐴 ⊆ (toCaraSiga‘𝑀))    &   (𝜑𝐸 ∈ 𝒫 𝑂)       (𝜑 → ((𝑀‘(𝐸 𝐴)) +𝑒 (𝑀‘(𝐸 𝐴))) ≤ (𝑀𝐸))
 
Theoremcarsgclctun 32297* The Caratheodory measurable sets are closed under countable union. (Contributed by Thierry Arnoux, 21-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)    &   ((𝜑𝑥 ≼ ω ∧ 𝑥 ⊆ 𝒫 𝑂) → (𝑀 𝑥) ≤ Σ*𝑦𝑥(𝑀𝑦))    &   ((𝜑𝑥𝑦𝑦 ∈ 𝒫 𝑂) → (𝑀𝑥) ≤ (𝑀𝑦))    &   (𝜑𝐴 ≼ ω)    &   (𝜑𝐴 ⊆ (toCaraSiga‘𝑀))       (𝜑 𝐴 ∈ (toCaraSiga‘𝑀))
 
Theoremcarsgsiga 32298* The Caratheodory measurable sets constructed from outer measures form a Sigma-algebra. Statement (iii) of Theorem 1.11.4 of [Bogachev] p. 42. (Contributed by Thierry Arnoux, 17-May-2020.)
(𝜑𝑂𝑉)    &   (𝜑𝑀:𝒫 𝑂⟶(0[,]+∞))    &   (𝜑 → (𝑀‘∅) = 0)    &   ((𝜑𝑥 ≼ ω ∧ 𝑥 ⊆ 𝒫 𝑂) → (𝑀 𝑥) ≤ Σ*𝑦𝑥(𝑀𝑦))    &   ((𝜑𝑥𝑦𝑦 ∈ 𝒫 𝑂) → (𝑀𝑥) ≤ (𝑀𝑦))       (𝜑 → (toCaraSiga‘𝑀) ∈ (sigAlgebra‘𝑂))
 
Theoremomsmeas 32299 The restriction of a constructed outer measure to Caratheodory measurable sets is a measure. This theorem allows to construct measures from pre-measures with the required characteristics, as for the Lebesgue measure. (Contributed by Thierry Arnoux, 17-May-2020.)
𝑀 = (toOMeas‘𝑅)    &   𝑆 = (toCaraSiga‘𝑀)    &   (𝜑𝑄𝑉)    &   (𝜑𝑅:𝑄⟶(0[,]+∞))    &   (𝜑 → ∅ ∈ dom 𝑅)    &   (𝜑 → (𝑅‘∅) = 0)       (𝜑 → (𝑀𝑆) ∈ (measures‘𝑆))
 
Theorempmeasmono 32300* This theorem's hypotheses define a pre-measure. A pre-measure is monotone. (Contributed by Thierry Arnoux, 19-Jul-2020.)
(𝜑𝑃:𝑅⟶(0[,]+∞))    &   (𝜑 → (𝑃‘∅) = 0)    &   ((𝜑 ∧ (𝑥 ≼ ω ∧ 𝑥𝑅Disj 𝑦𝑥 𝑦)) → (𝑃 𝑥) = Σ*𝑦𝑥(𝑃𝑦))    &   (𝜑𝐴𝑅)    &   (𝜑𝐵𝑅)    &   (𝜑 → (𝐵𝐴) ∈ 𝑅)    &   (𝜑𝐴𝐵)       (𝜑 → (𝑃𝐴) ≤ (𝑃𝐵))
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