Borel (measurable) space #
Main definitions #
borel α: the leastσ-algebra that contains all open sets;class borel_space: a space withtopological_spaceandmeasurable_spacestructures such that‹measurable_space α› = borel α;class opens_measurable_space: a space withtopological_spaceandmeasurable_spacestructures such that all open sets are measurable; equivalently,borel α ≤ ‹measurable_space α›.borel_spaceinstances onempty,unit,bool,nat,int,rat;measurableandborel_spaceinstances onℝ,ℝ≥0,ℝ≥0∞.- A measure is
regularif it is finite on compact sets, inner regular and outer regular.
Main statements #
is_open.measurable_set,is_closed.measurable_set: open and closed sets are measurable;continuous.measurable: a continuous function is measurable;continuous.measurable2: iff : α → βandg : α → γare measurable andop : β × γ → δis continuous, thenλ x, op (f x, g y)is measurable;measurable.addetc : dot notation for arithmetic operations onmeasurablepredicates, and similarly fordistandedist;ae_measurable.add: similar dot notation for almost everywhere measurable functions;measurable.ennreal*: special cases for arithmetic operations onℝ≥0∞.
measurable_space structure generated by topological_space.
Equations
- borel α = measurable_space.generate_from {s : set α | is_open s}
A space with measurable_space and topological_space structures such that
all open sets are measurable.
A space with measurable_space and topological_space structures such that
the σ-algebra of measurable sets is exactly the σ-algebra generated by open sets.
In a borel_space all open sets are measurable.
If s is a measurable set, then 𝓝[s] a is a measurably generated filter for
each a. This cannot be an instance because it depends on a non-instance hs : measurable_set s.
A continuous function from an opens_measurable_space to a borel_space
is measurable.
A continuous function from an opens_measurable_space to a borel_space
is ae-measurable.
A homeomorphism between two Borel spaces is a measurable equivalence.
Equations
- h.to_measurable_equiv = {to_equiv := h.to_equiv, measurable_to_fun := _, measurable_inv_fun := _}
liminf over a general filter is measurable. See measurable_liminf for the version over ℕ.
limsup over a general filter is measurable. See measurable_limsup for the version over ℕ.
liminf over ℕ is measurable. See measurable_liminf' for a version with a general filter.
limsup over ℕ is measurable. See measurable_limsup' for a version with a general filter.
Convert a homeomorph to a measurable_equiv.
Equations
- homemorph.to_measurable_equiv h = {to_equiv := h.to_equiv, measurable_to_fun := _, measurable_inv_fun := _}
Equations
Equations
Equations
Equations
The set of finite ℝ≥0∞ numbers is measurable_equiv to ℝ≥0.
ℝ≥0∞ is measurable_equiv to ℝ≥0 ⊕ unit.
Equations
- ennreal.ennreal_equiv_sum = {to_equiv := {to_fun := (equiv.option_equiv_sum_punit ℝ≥0).to_fun, inv_fun := (equiv.option_equiv_sum_punit ℝ≥0).inv_fun, left_inv := ennreal.ennreal_equiv_sum._proof_1, right_inv := ennreal.ennreal_equiv_sum._proof_2}, measurable_to_fun := ennreal.ennreal_equiv_sum._proof_3, measurable_inv_fun := ennreal.ennreal_equiv_sum._proof_4}
note: ℝ≥0∞ can probably be generalized in a future version of this lemma.
A limit (over a general filter) of measurable ℝ≥0 valued functions is measurable.
The assumption hs can be dropped using filter.is_countably_generated.has_antimono_basis, but we
don't need that case yet.
A sequential limit of measurable ℝ≥0 valued functions is measurable.
A limit (over a general filter) of measurable functions valued in a metric space is measurable.
The assumption hs can be dropped using filter.is_countably_generated.has_antimono_basis, but we
don't need that case yet.
A sequential limit of measurable functions valued in a metric space is measurable.
Equations
- lt_top_of_is_compact : ∀ ⦃K : set α⦄, is_compact K → ⇑μ K < ⊤
- outer_regular : ∀ ⦃A : set α⦄, measurable_set A → (⨅ (U : set α) (h : is_open U) (h2 : A ⊆ U), ⇑μ U) ≤ ⇑μ A
- inner_regular : ∀ ⦃U : set α⦄, is_open U → (⇑μ U ≤ ⨆ (K : set α) (h : is_compact K) (h2 : K ⊆ U), ⇑μ K)
A measure μ is regular if
- it is finite on all compact sets;
- it is outer regular:
μ(A) = inf { μ(U) | A ⊆ U open }forAmeasurable; - it is inner regular:
μ(U) = sup { μ(K) | K ⊆ U compact }forUopen.
A regular measure in a σ-compact space is σ-finite.