Documentation

Mathlib.MeasureTheory.Measure.Typeclasses

Classes of measures #

We introduce the following typeclasses for measures:

A measure μ is called finite if μ univ < ∞.

  • measure_univ_lt_top : μ Set.univ <
Instances
    instance MeasureTheory.Restrict.isFiniteMeasure {α : Type u_1} {m0 : MeasurableSpace α} {s : Set α} (μ : MeasureTheory.Measure α) [hs : Fact (μ s < )] :
    Equations
    • =
    @[simp]
    Equations
    • =
    theorem MeasureTheory.measure_compl_le_add_of_le_add {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} {t : Set α} [MeasureTheory.IsFiniteMeasure μ] (hs : MeasurableSet s) (ht : MeasurableSet t) {ε : ENNReal} (h : μ s μ t + ε) :
    μ t μ s + ε
    theorem MeasureTheory.measure_compl_le_add_iff {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} {t : Set α} [MeasureTheory.IsFiniteMeasure μ] (hs : MeasurableSet s) (ht : MeasurableSet t) {ε : ENNReal} :
    μ s μ t + ε μ t μ s + ε

    The measure of the whole space with respect to a finite measure, considered as ℝ≥0.

    Equations
    Instances For
      @[instance 50]
      Equations
      • =
      Equations
      • =
      theorem MeasureTheory.Measure.le_of_add_le_add_left {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {ν₁ : MeasureTheory.Measure α} {ν₂ : MeasureTheory.Measure α} [MeasureTheory.IsFiniteMeasure μ] (A2 : μ + ν₁ μ + ν₂) :
      ν₁ ν₂

      le_of_add_le_add_left is normally applicable to OrderedCancelAddCommMonoid, but it holds for measures with the additional assumption that μ is finite.

      theorem MeasureTheory.summable_measure_toReal {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [hμ : MeasureTheory.IsFiniteMeasure μ] {f : Set α} (hf₁ : ∀ (i : ), MeasurableSet (f i)) (hf₂ : Pairwise (Disjoint on f)) :
      Summable fun (x : ) => (μ (f x)).toReal
      theorem MeasureTheory.ae_iff_measure_eq {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.IsFiniteMeasure μ] {p : αProp} (hp : MeasureTheory.NullMeasurableSet {a : α | p a} μ) :
      (∀ᵐ (a : α) ∂μ, p a) μ {a : α | p a} = μ Set.univ
      theorem MeasureTheory.ae_mem_iff_measure_eq {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.IsFiniteMeasure μ] {s : Set α} (hs : MeasureTheory.NullMeasurableSet s μ) :
      (∀ᵐ (a : α) ∂μ, a s) μ s = μ Set.univ
      theorem MeasureTheory.tendsto_measure_biUnion_Ici_zero_of_pairwise_disjoint {X : Type u_5} [MeasurableSpace X] {μ : MeasureTheory.Measure X} [MeasureTheory.IsFiniteMeasure μ] {Es : Set X} (Es_mble : ∀ (i : ), MeasureTheory.NullMeasurableSet (Es i) μ) (Es_disj : Pairwise fun (n m : ) => Disjoint (Es n) (Es m)) :
      Filter.Tendsto (μ fun (n : ) => ⋃ (i : ), ⋃ (_ : i n), Es i) Filter.atTop (nhds 0)
      theorem MeasureTheory.abs_toReal_measure_sub_le_measure_symmDiff' {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} {t : Set α} (hs : MeasureTheory.NullMeasurableSet s μ) (ht : MeasureTheory.NullMeasurableSet t μ) (hs' : μ s ) (ht' : μ t ) :
      |(μ s).toReal - (μ t).toReal| (μ (symmDiff s t)).toReal
      theorem MeasureTheory.abs_toReal_measure_sub_le_measure_symmDiff {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} {t : Set α} [MeasureTheory.IsFiniteMeasure μ] (hs : MeasureTheory.NullMeasurableSet s μ) (ht : MeasureTheory.NullMeasurableSet t μ) :
      |(μ s).toReal - (μ t).toReal| (μ (symmDiff s t)).toReal
      instance MeasureTheory.instIsFiniteMeasureSumMeasure {α : Type u_1} {ι : Type u_4} {m0 : MeasurableSpace α} {s : Finset ι} {μ : ιMeasureTheory.Measure α} [∀ (i : ι), MeasureTheory.IsFiniteMeasure (μ i)] :
      MeasureTheory.IsFiniteMeasure (∑ is, μ i)
      Equations
      • =

      A measure μ is zero or a probability measure if μ univ = 0 or μ univ = 1. This class of measures appears naturally when conditioning on events, and many results which are true for probability measures hold more generally over this class.

      • measure_univ : μ Set.univ = 0 μ Set.univ = 1
      Instances
        @[simp]

        A measure μ is called a probability measure if μ univ = 1.

        • measure_univ : μ Set.univ = 1
        Instances
          @[instance 100]
          Equations
          • =

          Note that this is not quite as useful as it looks because the measure takes values in ℝ≥0∞. Thus the subtraction appearing is the truncated subtraction of ℝ≥0∞, rather than the better-behaved subtraction of .

          Note that this is not quite as useful as it looks because the measure takes values in ℝ≥0∞. Thus the subtraction appearing is the truncated subtraction of ℝ≥0∞, rather than the better-behaved subtraction of .

          @[simp]
          @[simp]
          theorem MeasureTheory.ae_iff_prob_eq_one {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.IsProbabilityMeasure μ] {p : αProp} (hp : Measurable p) :
          (∀ᵐ (a : α) ∂μ, p a) μ {a : α | p a} = 1
          theorem MeasureTheory.isProbabilityMeasure_comap {α : Type u_1} {β : Type u_2} {m0 : MeasurableSpace α} [MeasurableSpace β] {μ : MeasureTheory.Measure α} [MeasureTheory.IsProbabilityMeasure μ] {f : βα} (hf : Function.Injective f) (hf' : ∀ᵐ (a : α) ∂μ, a Set.range f) (hf'' : ∀ (s : Set β), MeasurableSet sMeasurableSet (f '' s)) :
          theorem MeasureTheory.prob_compl_lt_one_sub_of_lt_prob {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} [MeasureTheory.IsZeroOrProbabilityMeasure μ] {p : ENNReal} (hμs : p < μ s) (s_mble : MeasurableSet s) :
          μ s < 1 - p

          Measure μ has no atoms if the measure of each singleton is zero.

          NB: Wikipedia assumes that for any measurable set s with positive μ-measure, there exists a measurable t ⊆ s such that 0 < μ t < μ s. While this implies μ {x} = 0, the converse is not true.

          • measure_singleton : ∀ (x : α), μ {x} = 0
          Instances
            @[simp]
            theorem MeasureTheory.NoAtoms.measure_singleton {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [self : MeasureTheory.NoAtoms μ] (x : α) :
            μ {x} = 0
            theorem Set.Subsingleton.measure_zero {α : Type u_1} {m0 : MeasurableSpace α} {s : Set α} (hs : s.Subsingleton) (μ : MeasureTheory.Measure α) [MeasureTheory.NoAtoms μ] :
            μ s = 0
            theorem MeasureTheory.Measure.restrict_singleton' {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] {a : α} :
            μ.restrict {a} = 0
            Equations
            • =
            theorem Set.Countable.measure_zero {α : Type u_1} {m0 : MeasurableSpace α} {s : Set α} (h : s.Countable) (μ : MeasureTheory.Measure α) [MeasureTheory.NoAtoms μ] :
            μ s = 0
            theorem Set.Countable.ae_not_mem {α : Type u_1} {m0 : MeasurableSpace α} {s : Set α} (h : s.Countable) (μ : MeasureTheory.Measure α) [MeasureTheory.NoAtoms μ] :
            ∀ᵐ (x : α) ∂μ, xs
            theorem Set.Countable.measure_restrict_compl {α : Type u_1} {m0 : MeasurableSpace α} {s : Set α} (h : s.Countable) (μ : MeasureTheory.Measure α) [MeasureTheory.NoAtoms μ] :
            μ.restrict s = μ
            @[simp]
            theorem MeasureTheory.restrict_compl_singleton {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] (a : α) :
            μ.restrict {a} = μ
            theorem Set.Finite.measure_zero {α : Type u_1} {m0 : MeasurableSpace α} {s : Set α} (h : s.Finite) (μ : MeasureTheory.Measure α) [MeasureTheory.NoAtoms μ] :
            μ s = 0
            theorem Finset.measure_zero {α : Type u_1} {m0 : MeasurableSpace α} (s : Finset α) (μ : MeasureTheory.Measure α) [MeasureTheory.NoAtoms μ] :
            μ s = 0
            theorem MeasureTheory.insert_ae_eq_self {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] (a : α) (s : Set α) :
            insert a s =ᵐ[μ] s
            theorem MeasureTheory.Ioo_ae_eq_Ioc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            theorem MeasureTheory.Ioc_ae_eq_Icc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            theorem MeasureTheory.Ioo_ae_eq_Ico {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            theorem MeasureTheory.Ioo_ae_eq_Icc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            theorem MeasureTheory.Ico_ae_eq_Icc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            theorem MeasureTheory.Ico_ae_eq_Ioc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            theorem MeasureTheory.restrict_Iio_eq_restrict_Iic {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} :
            μ.restrict (Set.Iio a) = μ.restrict (Set.Iic a)
            theorem MeasureTheory.restrict_Ioi_eq_restrict_Ici {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} :
            μ.restrict (Set.Ioi a) = μ.restrict (Set.Ici a)
            theorem MeasureTheory.restrict_Ioo_eq_restrict_Ioc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            μ.restrict (Set.Ioo a b) = μ.restrict (Set.Ioc a b)
            theorem MeasureTheory.restrict_Ioc_eq_restrict_Icc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            μ.restrict (Set.Ioc a b) = μ.restrict (Set.Icc a b)
            theorem MeasureTheory.restrict_Ioo_eq_restrict_Ico {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            μ.restrict (Set.Ioo a b) = μ.restrict (Set.Ico a b)
            theorem MeasureTheory.restrict_Ioo_eq_restrict_Icc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            μ.restrict (Set.Ioo a b) = μ.restrict (Set.Icc a b)
            theorem MeasureTheory.restrict_Ico_eq_restrict_Icc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            μ.restrict (Set.Ico a b) = μ.restrict (Set.Icc a b)
            theorem MeasureTheory.restrict_Ico_eq_restrict_Ioc {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [PartialOrder α] {a : α} {b : α} :
            μ.restrict (Set.Ico a b) = μ.restrict (Set.Ioc a b)
            theorem MeasureTheory.uIoc_ae_eq_interval {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.NoAtoms μ] [LinearOrder α] {a : α} {b : α} :
            Ι a b =ᵐ[μ] Set.uIcc a b
            theorem MeasureTheory.ite_ae_eq_of_measure_zero {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {γ : Type u_5} (f : αγ) (g : αγ) (s : Set α) [DecidablePred fun (x : α) => x s] (hs_zero : μ s = 0) :
            (fun (x : α) => if x s then f x else g x) =ᵐ[μ] g
            theorem MeasureTheory.ite_ae_eq_of_measure_compl_zero {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {γ : Type u_5} (f : αγ) (g : αγ) (s : Set α) [DecidablePred fun (x : α) => x s] (hs_zero : μ s = 0) :
            (fun (x : α) => if x s then f x else g x) =ᵐ[μ] f

            A measure is called finite at filter f if it is finite at some set s ∈ f. Equivalently, it is eventually finite at s in f.small_sets.

            Equations
            • μ.FiniteAtFilter f = sf, μ s <
            Instances For
              theorem MeasureTheory.Measure.FiniteAtFilter.exists_mem_basis {α : Type u_1} {ι : Type u_4} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} (hμ : μ.FiniteAtFilter f) {p : ιProp} {s : ιSet α} (hf : f.HasBasis p s) :
              ∃ (i : ι), p i μ (s i) <
              theorem MeasureTheory.Measure.finiteAtBot {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) :
              μ.FiniteAtFilter
              structure MeasureTheory.Measure.FiniteSpanningSetsIn {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) (C : Set (Set α)) :
              Type u_1

              μ has finite spanning sets in C if there is a countable sequence of sets in C that have finite measures. This structure is a type, which is useful if we want to record extra properties about the sets, such as that they are monotone. SigmaFinite is defined in terms of this: μ is σ-finite if there exists a sequence of finite spanning sets in the collection of all measurable sets.

              • set : Set α
              • set_mem : ∀ (i : ), self.set i C
              • finite : ∀ (i : ), μ (self.set i) <
              • spanning : ⋃ (i : ), self.set i = Set.univ
              Instances For
                theorem MeasureTheory.Measure.FiniteSpanningSetsIn.set_mem {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {C : Set (Set α)} (self : μ.FiniteSpanningSetsIn C) (i : ) :
                self.set i C
                theorem MeasureTheory.Measure.FiniteSpanningSetsIn.finite {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {C : Set (Set α)} (self : μ.FiniteSpanningSetsIn C) (i : ) :
                μ (self.set i) <
                theorem MeasureTheory.Measure.FiniteSpanningSetsIn.spanning {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {C : Set (Set α)} (self : μ.FiniteSpanningSetsIn C) :
                ⋃ (i : ), self.set i = Set.univ

                A measure is called s-finite if it is a countable sum of finite measures.

                Instances

                  A sequence of finite measures such that μ = sum (sFiniteSeq μ) (see sum_sFiniteSeq).

                  Equations
                  Instances For
                    @[simp]

                    A countable sum of finite measures is s-finite. This lemma is superseded by the instance below.

                    Equations
                    • =
                    Equations
                    • =
                    theorem MeasureTheory.exists_isFiniteMeasure_absolutelyContinuous {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) [MeasureTheory.SFinite μ] :
                    ∃ (ν : MeasureTheory.Measure α), MeasureTheory.IsFiniteMeasure ν μ.AbsolutelyContinuous ν ν.AbsolutelyContinuous μ

                    For an s-finite measure μ, there exists a finite measure ν such that each of μ and ν is absolutely continuous with respect to the other.

                    @[deprecated MeasureTheory.exists_isFiniteMeasure_absolutelyContinuous]

                    A measure μ is called σ-finite if there is a countable collection of sets { A i | i ∈ ℕ } such that μ (A i) < ∞ and ⋃ i, A i = s.

                    • out' : Nonempty (μ.FiniteSpanningSetsIn Set.univ)
                    Instances
                      theorem MeasureTheory.SigmaFinite.out' {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [self : MeasureTheory.SigmaFinite μ] :
                      Nonempty (μ.FiniteSpanningSetsIn Set.univ)
                      theorem MeasureTheory.sigmaFinite_iff {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} :
                      MeasureTheory.SigmaFinite μ Nonempty (μ.FiniteSpanningSetsIn Set.univ)
                      theorem MeasureTheory.SigmaFinite.out {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} (h : MeasureTheory.SigmaFinite μ) :
                      Nonempty (μ.FiniteSpanningSetsIn Set.univ)
                      def MeasureTheory.Measure.toFiniteSpanningSetsIn {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) [h : MeasureTheory.SigmaFinite μ] :
                      μ.FiniteSpanningSetsIn {s : Set α | MeasurableSet s}

                      If μ is σ-finite it has finite spanning sets in the collection of all measurable sets.

                      Equations
                      • μ.toFiniteSpanningSetsIn = { set := fun (n : ) => MeasureTheory.toMeasurable μ (.some.set n), set_mem := , finite := , spanning := }
                      Instances For

                        A noncomputable way to get a monotone collection of sets that span univ and have finite measure using Classical.choose. This definition satisfies monotonicity in addition to all other properties in SigmaFinite.

                        Equations
                        Instances For
                          noncomputable def MeasureTheory.spanningSetsIndex {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) [MeasureTheory.SigmaFinite μ] (x : α) :

                          spanningSetsIndex μ x is the least n : ℕ such that x ∈ spanningSets μ n.

                          Equations
                          Instances For
                            theorem MeasureTheory.eventually_mem_spanningSets {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) [MeasureTheory.SigmaFinite μ] (x : α) :
                            ∀ᶠ (n : ) in Filter.atTop, x MeasureTheory.spanningSets μ n

                            A set in a σ-finite space has zero measure if and only if its intersection with all members of the countable family of finite measure spanning sets has zero measure.

                            A set in a σ-finite space has positive measure if and only if its intersection with some member of the countable family of finite measure spanning sets has positive measure.

                            theorem MeasureTheory.Measure.finite_const_le_meas_of_disjoint_iUnion₀ {α : Type u_1} {ι : Type u_5} [MeasurableSpace α] (μ : MeasureTheory.Measure α) {ε : ENNReal} (ε_pos : 0 < ε) {As : ιSet α} (As_mble : ∀ (i : ι), MeasureTheory.NullMeasurableSet (As i) μ) (As_disj : Pairwise (MeasureTheory.AEDisjoint μ on As)) (Union_As_finite : μ (⋃ (i : ι), As i) ) :
                            {i : ι | ε μ (As i)}.Finite

                            If the union of a.e.-disjoint null-measurable sets has finite measure, then there are only finitely many members of the union whose measure exceeds any given positive number.

                            theorem MeasureTheory.Measure.finite_const_le_meas_of_disjoint_iUnion {α : Type u_1} {ι : Type u_5} [MeasurableSpace α] (μ : MeasureTheory.Measure α) {ε : ENNReal} (ε_pos : 0 < ε) {As : ιSet α} (As_mble : ∀ (i : ι), MeasurableSet (As i)) (As_disj : Pairwise (Disjoint on As)) (Union_As_finite : μ (⋃ (i : ι), As i) ) :
                            {i : ι | ε μ (As i)}.Finite

                            If the union of disjoint measurable sets has finite measure, then there are only finitely many members of the union whose measure exceeds any given positive number.

                            theorem Set.Infinite.meas_eq_top {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasurableSingletonClass α] {s : Set α} (hs : s.Infinite) (h' : ∃ (ε : ENNReal), ε 0 xs, ε μ {x}) :
                            μ s =

                            If all elements of an infinite set have measure uniformly separated from zero, then the set has infinite measure.

                            theorem MeasureTheory.Measure.countable_meas_pos_of_disjoint_of_meas_iUnion_ne_top₀ {α : Type u_1} {ι : Type u_5} :
                            ∀ {x : MeasurableSpace α} (μ : MeasureTheory.Measure α) {As : ιSet α}, (∀ (i : ι), MeasureTheory.NullMeasurableSet (As i) μ)Pairwise (MeasureTheory.AEDisjoint μ on As)μ (⋃ (i : ι), As i) {i : ι | 0 < μ (As i)}.Countable

                            If the union of a.e.-disjoint null-measurable sets has finite measure, then there are only countably many members of the union whose measure is positive.

                            theorem MeasureTheory.Measure.countable_meas_pos_of_disjoint_of_meas_iUnion_ne_top {α : Type u_1} {ι : Type u_5} :
                            ∀ {x : MeasurableSpace α} (μ : MeasureTheory.Measure α) {As : ιSet α}, (∀ (i : ι), MeasurableSet (As i))Pairwise (Disjoint on As)μ (⋃ (i : ι), As i) {i : ι | 0 < μ (As i)}.Countable

                            If the union of disjoint measurable sets has finite measure, then there are only countably many members of the union whose measure is positive.

                            theorem MeasureTheory.Measure.countable_meas_pos_of_disjoint_iUnion₀ {α : Type u_1} {ι : Type u_5} :
                            ∀ {x : MeasurableSpace α} {μ : MeasureTheory.Measure α} [inst : MeasureTheory.SFinite μ] {As : ιSet α}, (∀ (i : ι), MeasureTheory.NullMeasurableSet (As i) μ)Pairwise (MeasureTheory.AEDisjoint μ on As){i : ι | 0 < μ (As i)}.Countable

                            In an s-finite space, among disjoint null-measurable sets, only countably many can have positive measure.

                            theorem MeasureTheory.Measure.countable_meas_pos_of_disjoint_iUnion {α : Type u_1} {ι : Type u_5} :
                            ∀ {x : MeasurableSpace α} {μ : MeasureTheory.Measure α} [inst : MeasureTheory.SFinite μ] {As : ιSet α}, (∀ (i : ι), MeasurableSet (As i))Pairwise (Disjoint on As){i : ι | 0 < μ (As i)}.Countable

                            In an s-finite space, among disjoint measurable sets, only countably many can have positive measure.

                            theorem MeasureTheory.Measure.countable_meas_level_set_pos₀ {α : Type u_5} {β : Type u_6} :
                            ∀ {x : MeasurableSpace α} {μ : MeasureTheory.Measure α} [inst : MeasureTheory.SFinite μ] [inst : MeasurableSpace β] [inst_1 : MeasurableSingletonClass β] {g : αβ}, MeasureTheory.NullMeasurable g μ{t : β | 0 < μ {a : α | g a = t}}.Countable
                            theorem MeasureTheory.Measure.countable_meas_level_set_pos {α : Type u_5} {β : Type u_6} :
                            ∀ {x : MeasurableSpace α} {μ : MeasureTheory.Measure α} [inst : MeasureTheory.SFinite μ] [inst : MeasurableSpace β] [inst_1 : MeasurableSingletonClass β] {g : αβ}, Measurable g{t : β | 0 < μ {a : α | g a = t}}.Countable
                            theorem MeasureTheory.Measure.measure_toMeasurable_inter_of_sum {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} (hs : MeasurableSet s) {t : Set α} {m : MeasureTheory.Measure α} (hv : ∀ (n : ), (m n) t ) (hμ : μ = MeasureTheory.Measure.sum m) :
                            μ (MeasureTheory.toMeasurable μ t s) = μ (t s)

                            If a measure μ is the sum of a countable family mₙ, and a set t has finite measure for each mₙ, then its measurable superset toMeasurable μ t (which has the same measure as t) satisfies, for any measurable set s, the equality μ (toMeasurable μ t ∩ s) = μ (t ∩ s).

                            theorem MeasureTheory.Measure.measure_toMeasurable_inter_of_cover {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} (hs : MeasurableSet s) {t : Set α} {v : Set α} (hv : t ⋃ (n : ), v n) (h'v : ∀ (n : ), μ (t v n) ) :
                            μ (MeasureTheory.toMeasurable μ t s) = μ (t s)

                            If a set t is covered by a countable family of finite measure sets, then its measurable superset toMeasurable μ t (which has the same measure as t) satisfies, for any measurable set s, the equality μ (toMeasurable μ t ∩ s) = μ (t ∩ s).

                            theorem MeasureTheory.Measure.restrict_toMeasurable_of_cover {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} {v : Set α} (hv : s ⋃ (n : ), v n) (h'v : ∀ (n : ), μ (s v n) ) :
                            μ.restrict (MeasureTheory.toMeasurable μ s) = μ.restrict s

                            The measurable superset toMeasurable μ t of t (which has the same measure as t) satisfies, for any measurable set s, the equality μ (toMeasurable μ t ∩ s) = μ (t ∩ s). This only holds when μ is s-finite -- for example for σ-finite measures. For a version without this assumption (but requiring that t has finite measure), see measure_toMeasurable_inter.

                            @[simp]
                            theorem MeasureTheory.Measure.exists_subset_measure_lt_top {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} [MeasureTheory.SigmaFinite μ] {r : ENNReal} (hs : MeasurableSet s) (h's : r < μ s) :
                            ∃ (t : Set α), MeasurableSet t t s r < μ t μ t <

                            In a σ-finite space, any measurable set of measure > r contains a measurable subset of finite measure > r.

                            def MeasureTheory.Measure.FiniteSpanningSetsIn.mono' {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {C : Set (Set α)} {D : Set (Set α)} (h : μ.FiniteSpanningSetsIn C) (hC : C {s : Set α | μ s < } D) :
                            μ.FiniteSpanningSetsIn D

                            If μ has finite spanning sets in C and C ∩ {s | μ s < ∞} ⊆ D then μ has finite spanning sets in D.

                            Equations
                            • h.mono' hC = { set := h.set, set_mem := , finite := , spanning := }
                            Instances For
                              def MeasureTheory.Measure.FiniteSpanningSetsIn.mono {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {C : Set (Set α)} {D : Set (Set α)} (h : μ.FiniteSpanningSetsIn C) (hC : C D) :
                              μ.FiniteSpanningSetsIn D

                              If μ has finite spanning sets in C and C ⊆ D then μ has finite spanning sets in D.

                              Equations
                              • h.mono hC = h.mono'
                              Instances For
                                theorem MeasureTheory.Measure.FiniteSpanningSetsIn.sigmaFinite {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {C : Set (Set α)} (h : μ.FiniteSpanningSetsIn C) :

                                If μ has finite spanning sets in the collection of measurable sets C, then μ is σ-finite.

                                theorem MeasureTheory.Measure.FiniteSpanningSetsIn.ext {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {ν : MeasureTheory.Measure α} {C : Set (Set α)} (hA : m0 = MeasurableSpace.generateFrom C) (hC : IsPiSystem C) (h : μ.FiniteSpanningSetsIn C) (h_eq : sC, μ s = ν s) :
                                μ = ν

                                An extensionality for measures. It is ext_of_generateFrom_of_iUnion formulated in terms of FiniteSpanningSetsIn.

                                theorem MeasureTheory.Measure.FiniteSpanningSetsIn.isCountablySpanning {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {C : Set (Set α)} (h : μ.FiniteSpanningSetsIn C) :
                                theorem MeasureTheory.Measure.sigmaFinite_of_countable {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {S : Set (Set α)} (hc : S.Countable) (hμ : sS, μ s < ) (hU : ⋃₀ S = Set.univ) :
                                def MeasureTheory.Measure.FiniteSpanningSetsIn.ofLE {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {ν : MeasureTheory.Measure α} (h : ν μ) {C : Set (Set α)} (S : μ.FiniteSpanningSetsIn C) :
                                ν.FiniteSpanningSetsIn C

                                Given measures μ, ν where ν ≤ μ, FiniteSpanningSetsIn.ofLe provides the induced FiniteSpanningSet with respect to ν from a FiniteSpanningSet with respect to μ.

                                Equations
                                Instances For
                                  @[simp]
                                  theorem MeasureTheory.Measure.add_right_inj {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) (ν₁ : MeasureTheory.Measure α) (ν₂ : MeasureTheory.Measure α) [MeasureTheory.SigmaFinite μ] :
                                  μ + ν₁ = μ + ν₂ ν₁ = ν₂
                                  @[simp]
                                  theorem MeasureTheory.Measure.add_left_inj {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) (ν₁ : MeasureTheory.Measure α) (ν₂ : MeasureTheory.Measure α) [MeasureTheory.SigmaFinite μ] :
                                  ν₁ + μ = ν₂ + μ ν₁ = ν₂
                                  @[instance 100]

                                  Every finite measure is σ-finite.

                                  Equations
                                  • =
                                  Equations
                                  • =
                                  Equations
                                  • =
                                  instance MeasureTheory.instSigmaFiniteRestrictUnionSet {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} {t : Set α} [MeasureTheory.SigmaFinite (μ.restrict s)] [MeasureTheory.SigmaFinite (μ.restrict t)] :
                                  MeasureTheory.SigmaFinite (μ.restrict (s t))
                                  Equations
                                  • =
                                  instance MeasureTheory.instSigmaFiniteRestrictInterSet {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} {t : Set α} [MeasureTheory.SigmaFinite (μ.restrict s)] :
                                  MeasureTheory.SigmaFinite (μ.restrict (s t))
                                  Equations
                                  • =
                                  instance MeasureTheory.instSigmaFiniteRestrictInterSet_1 {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} {t : Set α} [MeasureTheory.SigmaFinite (μ.restrict t)] :
                                  MeasureTheory.SigmaFinite (μ.restrict (s t))
                                  Equations
                                  • =
                                  theorem MeasureTheory.ae_of_forall_measure_lt_top_ae_restrict' {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} (ν : MeasureTheory.Measure α) [MeasureTheory.SigmaFinite μ] [MeasureTheory.SigmaFinite ν] (P : αProp) (h : ∀ (s : Set α), MeasurableSet sμ s < ν s < ∀ᵐ (x : α) ∂μ.restrict s, P x) :
                                  ∀ᵐ (x : α) ∂μ, P x

                                  Similar to ae_of_forall_measure_lt_top_ae_restrict, but where you additionally get the hypothesis that another σ-finite measure has finite values on s.

                                  theorem MeasureTheory.ae_of_forall_measure_lt_top_ae_restrict {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [MeasureTheory.SigmaFinite μ] (P : αProp) (h : ∀ (s : Set α), MeasurableSet sμ s < ∀ᵐ (x : α) ∂μ.restrict s, P x) :
                                  ∀ᵐ (x : α) ∂μ, P x

                                  To prove something for almost all x w.r.t. a σ-finite measure, it is sufficient to show that this holds almost everywhere in sets where the measure has finite value.

                                  A measure is called locally finite if it is finite in some neighborhood of each point.

                                  • finiteAtNhds : ∀ (x : α), μ.FiniteAtFilter (nhds x)
                                  Instances
                                    theorem MeasureTheory.IsLocallyFiniteMeasure.finiteAtNhds {α : Type u_1} {m0 : MeasurableSpace α} :
                                    ∀ {inst : TopologicalSpace α} {μ : MeasureTheory.Measure α} [self : MeasureTheory.IsLocallyFiniteMeasure μ] (x : α), μ.FiniteAtFilter (nhds x)

                                    A measure μ is finite on compacts if any compact set K satisfies μ K < ∞.

                                    Instances

                                      A compact subset has finite measure for a measure which is finite on compacts.

                                      A compact subset has finite measure for a measure which is finite on compacts.

                                      A bounded subset has finite measure for a measure which is finite on compact sets, in a proper space.

                                      @[instance 100]

                                      A measure which is finite on compact sets in a locally compact space is locally finite.

                                      Equations
                                      • =
                                      theorem MeasureTheory.exists_pos_measure_of_cover {α : Type u_1} {ι : Type u_4} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [Countable ι] {U : ιSet α} (hU : ⋃ (i : ι), U i = Set.univ) (hμ : μ 0) :
                                      ∃ (i : ι), 0 < μ (U i)
                                      theorem MeasureTheory.exists_pos_preimage_ball {α : Type u_1} {δ : Type u_3} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [PseudoMetricSpace δ] (f : αδ) (x : δ) (hμ : μ 0) :
                                      ∃ (n : ), 0 < μ (f ⁻¹' Metric.ball x n)
                                      theorem MeasureTheory.exists_pos_ball {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} [PseudoMetricSpace α] (x : α) (hμ : μ 0) :
                                      ∃ (n : ), 0 < μ (Metric.ball x n)
                                      @[deprecated MeasureTheory.measure_null_of_locally_null]
                                      theorem MeasureTheory.null_of_locally_null {α : Type u_1} {F : Type u_3} [FunLike F (Set α) ENNReal] [MeasureTheory.OuterMeasureClass F α] {μ : F} [TopologicalSpace α] [SecondCountableTopology α] (s : Set α) (hs : xs, unhdsWithin x s, μ u = 0) :
                                      μ s = 0

                                      If a set has zero measure in a neighborhood of each of its points, then it has zero measure in a second-countable space.

                                      theorem MeasureTheory.exists_ne_forall_mem_nhds_pos_measure_preimage {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {β : Type u_5} [TopologicalSpace β] [T1Space β] [SecondCountableTopology β] [Nonempty β] {f : αβ} (h : ∀ (b : β), ∃ᵐ (x : α) ∂μ, f x b) :
                                      ∃ (a : β) (b : β), a b (∀ snhds a, 0 < μ (f ⁻¹' s)) tnhds b, 0 < μ (f ⁻¹' t)
                                      theorem MeasureTheory.ext_on_measurableSpace_of_generate_finite {α : Type u_5} (m₀ : MeasurableSpace α) {μ : MeasureTheory.Measure α} {ν : MeasureTheory.Measure α} [MeasureTheory.IsFiniteMeasure μ] (C : Set (Set α)) (hμν : sC, μ s = ν s) {m : MeasurableSpace α} (h : m m₀) (hA : m = MeasurableSpace.generateFrom C) (hC : IsPiSystem C) (h_univ : μ Set.univ = ν Set.univ) {s : Set α} (hs : MeasurableSet s) :
                                      μ s = ν s

                                      If two finite measures give the same mass to the whole space and coincide on a π-system made of measurable sets, then they coincide on all sets in the σ-algebra generated by the π-system.

                                      theorem MeasureTheory.ext_of_generate_finite {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {ν : MeasureTheory.Measure α} (C : Set (Set α)) (hA : m0 = MeasurableSpace.generateFrom C) (hC : IsPiSystem C) [MeasureTheory.IsFiniteMeasure μ] (hμν : sC, μ s = ν s) (h_univ : μ Set.univ = ν Set.univ) :
                                      μ = ν

                                      Two finite measures are equal if they are equal on the π-system generating the σ-algebra (and univ).

                                      def MeasureTheory.Measure.FiniteSpanningSetsIn.disjointed {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} (S : μ.FiniteSpanningSetsIn {s : Set α | MeasurableSet s}) :
                                      μ.FiniteSpanningSetsIn {s : Set α | MeasurableSet s}

                                      Given S : μ.FiniteSpanningSetsIn {s | MeasurableSet s}, FiniteSpanningSetsIn.disjointed provides a FiniteSpanningSetsIn {s | MeasurableSet s} such that its underlying sets are pairwise disjoint.

                                      Equations
                                      • S.disjointed = { set := disjointed S.set, set_mem := , finite := , spanning := }
                                      Instances For
                                        theorem MeasureTheory.Measure.FiniteSpanningSetsIn.disjointed_set_eq {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} (S : μ.FiniteSpanningSetsIn {s : Set α | MeasurableSet s}) :
                                        S.disjointed.set = disjointed S.set
                                        theorem MeasureTheory.Measure.exists_eq_disjoint_finiteSpanningSetsIn {α : Type u_1} {m0 : MeasurableSpace α} (μ : MeasureTheory.Measure α) (ν : MeasureTheory.Measure α) [MeasureTheory.SigmaFinite μ] [MeasureTheory.SigmaFinite ν] :
                                        ∃ (S : μ.FiniteSpanningSetsIn {s : Set α | MeasurableSet s}) (T : ν.FiniteSpanningSetsIn {s : Set α | MeasurableSet s}), S.set = T.set Pairwise (Disjoint on S.set)
                                        theorem MeasureTheory.Measure.FiniteAtFilter.filter_mono {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} {g : Filter α} (h : f g) :
                                        μ.FiniteAtFilter gμ.FiniteAtFilter f
                                        theorem MeasureTheory.Measure.FiniteAtFilter.inf_of_left {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} {g : Filter α} (h : μ.FiniteAtFilter f) :
                                        μ.FiniteAtFilter (f g)
                                        theorem MeasureTheory.Measure.FiniteAtFilter.inf_of_right {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} {g : Filter α} (h : μ.FiniteAtFilter g) :
                                        μ.FiniteAtFilter (f g)
                                        @[simp]
                                        theorem MeasureTheory.Measure.FiniteAtFilter.inf_ae_iff {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} :
                                        μ.FiniteAtFilter (f MeasureTheory.ae μ) μ.FiniteAtFilter f
                                        theorem MeasureTheory.Measure.FiniteAtFilter.of_inf_ae {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} :
                                        μ.FiniteAtFilter (f MeasureTheory.ae μ)μ.FiniteAtFilter f

                                        Alias of the forward direction of MeasureTheory.Measure.FiniteAtFilter.inf_ae_iff.

                                        theorem MeasureTheory.Measure.FiniteAtFilter.filter_mono_ae {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} {g : Filter α} (h : f MeasureTheory.ae μ g) (hg : μ.FiniteAtFilter g) :
                                        μ.FiniteAtFilter f
                                        theorem MeasureTheory.Measure.FiniteAtFilter.measure_mono {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {ν : MeasureTheory.Measure α} {f : Filter α} (h : μ ν) :
                                        ν.FiniteAtFilter fμ.FiniteAtFilter f
                                        theorem MeasureTheory.Measure.FiniteAtFilter.mono {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {ν : MeasureTheory.Measure α} {f : Filter α} {g : Filter α} (hf : f g) (hμ : μ ν) :
                                        ν.FiniteAtFilter gμ.FiniteAtFilter f
                                        theorem MeasureTheory.Measure.FiniteAtFilter.eventually {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} (h : μ.FiniteAtFilter f) :
                                        ∀ᶠ (s : Set α) in f.smallSets, μ s <
                                        theorem MeasureTheory.Measure.FiniteAtFilter.filterSup {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : Filter α} {g : Filter α} :
                                        μ.FiniteAtFilter fμ.FiniteAtFilter gμ.FiniteAtFilter (f g)
                                        @[simp]
                                        theorem MeasureTheory.Measure.finiteAt_principal {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {s : Set α} :
                                        μ.FiniteAtFilter (Filter.principal s) μ s <
                                        theorem IsCompact.exists_open_superset_measure_lt_top' {α : Type u_1} [TopologicalSpace α] [MeasurableSpace α] {μ : MeasureTheory.Measure α} {s : Set α} (h : IsCompact s) (hμ : xs, μ.FiniteAtFilter (nhds x)) :
                                        Us, IsOpen U μ U <

                                        If s is a compact set and μ is finite at 𝓝 x for every x ∈ s, then s admits an open superset of finite measure.

                                        If s is a compact set and μ is a locally finite measure, then s admits an open superset of finite measure.

                                        theorem IsCompact.measure_lt_top_of_nhdsWithin {α : Type u_1} [TopologicalSpace α] [MeasurableSpace α] {μ : MeasureTheory.Measure α} {s : Set α} (h : IsCompact s) (hμ : xs, μ.FiniteAtFilter (nhdsWithin x s)) :
                                        μ s <
                                        theorem IsCompact.measure_zero_of_nhdsWithin {α : Type u_1} [TopologicalSpace α] [MeasurableSpace α] {μ : MeasureTheory.Measure α} {s : Set α} (hs : IsCompact s) :
                                        (∀ as, tnhdsWithin a s, μ t = 0)μ s = 0
                                        def MeasureTheory.Measure.finiteSpanningSetsInCompact {α : Type u_1} [TopologicalSpace α] [SigmaCompactSpace α] :
                                        {x : MeasurableSpace α} → (μ : MeasureTheory.Measure α) → [inst : MeasureTheory.IsLocallyFiniteMeasure μ] → μ.FiniteSpanningSetsIn {K : Set α | IsCompact K}

                                        Compact covering of a σ-compact topological space as MeasureTheory.Measure.FiniteSpanningSetsIn.

                                        Equations
                                        • μ.finiteSpanningSetsInCompact = { set := compactCovering α, set_mem := , finite := , spanning := }
                                        Instances For
                                          def MeasureTheory.Measure.finiteSpanningSetsInOpen {α : Type u_1} [TopologicalSpace α] [SigmaCompactSpace α] :
                                          {x : MeasurableSpace α} → (μ : MeasureTheory.Measure α) → [inst : MeasureTheory.IsLocallyFiniteMeasure μ] → μ.FiniteSpanningSetsIn {K : Set α | IsOpen K}

                                          A locally finite measure on a σ-compact topological space admits a finite spanning sequence of open sets.

                                          Equations
                                          • μ.finiteSpanningSetsInOpen = { set := fun (n : ) => .choose, set_mem := , finite := , spanning := }
                                          Instances For
                                            @[irreducible]

                                            A locally finite measure on a second countable topological space admits a finite spanning sequence of open sets.

                                            Equations
                                            Instances For