Independence with respect to a kernel and a measure #
A family of sets of sets π : ι → Set (Set Ω) is independent with respect to a kernel
κ : kernel α Ω and a measure μ on α if for any finite set of indices s = {i_1, ..., i_n},
for any sets f i_1 ∈ π i_1, ..., f i_n ∈ π i_n, then for μ-almost every a : α,
κ a (⋂ i in s, f i) = ∏ i ∈ s, κ a (f i).
This notion of independence is a generalization of both independence and conditional independence.
For conditional independence, κ is the conditional kernel ProbabilityTheory.condexpKernel and
μ is the ambiant measure. For (non-conditional) independence, κ = kernel.const Unit μ and the
measure is the Dirac measure on Unit.
The main purpose of this file is to prove only once the properties that hold for both conditional and non-conditional independence.
Main definitions #
ProbabilityTheory.kernel.iIndepSets: independence of a family of sets of sets. Variant for two sets of sets:ProbabilityTheory.kernel.IndepSets.ProbabilityTheory.kernel.iIndep: independence of a family of σ-algebras. Variant for two σ-algebras:Indep.ProbabilityTheory.kernel.iIndepSet: independence of a family of sets. Variant for two sets:ProbabilityTheory.kernel.IndepSet.ProbabilityTheory.kernel.iIndepFun: independence of a family of functions (random variables). Variant for two functions:ProbabilityTheory.kernel.IndepFun.
See the file Mathlib/Probability/Kernel/Basic.lean for a more detailed discussion of these
definitions in the particular case of the usual independence notion.
Main statements #
ProbabilityTheory.kernel.iIndepSets.iIndep: if π-systems are independent as sets of sets, then the measurable space structures they generate are independent.ProbabilityTheory.kernel.IndepSets.Indep: variant with two π-systems.
A family of sets of sets π : ι → Set (Set Ω) is independent with respect to a kernel κ and
a measure μ if for any finite set of indices s = {i_1, ..., i_n}, for any sets
f i_1 ∈ π i_1, ..., f i_n ∈ π i_n, then ∀ᵐ a ∂μ, κ a (⋂ i in s, f i) = ∏ i ∈ s, κ a (f i).
It will be used for families of pi_systems.
Equations
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Two sets of sets s₁, s₂ are independent with respect to a kernel κ and a measure μ if for
any sets t₁ ∈ s₁, t₂ ∈ s₂, then ∀ᵐ a ∂μ, κ a (t₁ ∩ t₂) = κ a (t₁) * κ a (t₂)
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A family of measurable space structures (i.e. of σ-algebras) is independent with respect to a
kernel κ and a measure μ if the family of sets of measurable sets they define is independent.
Equations
- ProbabilityTheory.kernel.iIndep m κ μ = ProbabilityTheory.kernel.iIndepSets (fun (x : ι) => {s : Set Ω | MeasurableSet s}) κ μ
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Two measurable space structures (or σ-algebras) m₁, m₂ are independent with respect to a
kernel κ and a measure μ if for any sets t₁ ∈ m₁, t₂ ∈ m₂,
∀ᵐ a ∂μ, κ a (t₁ ∩ t₂) = κ a (t₁) * κ a (t₂)
Equations
- ProbabilityTheory.kernel.Indep m₁ m₂ κ μ = ProbabilityTheory.kernel.IndepSets {s : Set Ω | MeasurableSet s} {s : Set Ω | MeasurableSet s} κ μ
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A family of sets is independent if the family of measurable space structures they generate is
independent. For a set s, the generated measurable space has measurable sets ∅, s, sᶜ, univ.
Equations
- ProbabilityTheory.kernel.iIndepSet s κ μ = ProbabilityTheory.kernel.iIndep (fun (i : ι) => MeasurableSpace.generateFrom {s i}) κ μ
Instances For
Two sets are independent if the two measurable space structures they generate are independent.
For a set s, the generated measurable space structure has measurable sets ∅, s, sᶜ, univ.
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A family of functions defined on the same space Ω and taking values in possibly different
spaces, each with a measurable space structure, is independent if the family of measurable space
structures they generate on Ω is independent. For a function g with codomain having measurable
space structure m, the generated measurable space structure is MeasurableSpace.comap g m.
Equations
- ProbabilityTheory.kernel.iIndepFun m f κ μ = ProbabilityTheory.kernel.iIndep (fun (x : ι) => MeasurableSpace.comap (f x) (m x)) κ μ
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Two functions are independent if the two measurable space structures they generate are
independent. For a function f with codomain having measurable space structure m, the generated
measurable space structure is MeasurableSpace.comap f m.
Equations
- ProbabilityTheory.kernel.IndepFun f g κ μ = ProbabilityTheory.kernel.Indep (MeasurableSpace.comap f mβ) (MeasurableSpace.comap g mγ) κ μ
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π-system lemma #
Independence of measurable spaces is equivalent to independence of generating π-systems.
Independence of measurable space structures implies independence of generating π-systems #
Independence of generating π-systems implies independence of measurable space structures #
The measurable space structures generated by independent pi-systems are independent.
The measurable space structures generated by independent pi-systems are independent.
Independence of measurable sets #
We prove the following equivalences on IndepSet, for measurable sets s, t.
Independence of random variables #
If f is a family of mutually independent random variables (iIndepFun m f μ) and S, T are
two disjoint finite index sets, then the tuple formed by f i for i ∈ S is independent of the
tuple (f i)_i for i ∈ T.