English
If s is null-measurable, then almost surely x ∈ s under μ.restrict s.
Русский
Если s нулево измеримо, то почти наверняка x принадлежит s при μ ограниченной до s.
LaTeX
$$$\text{NullMeasurableSet}(s, μ) \Rightarrow \forall^\mathrm{a.e.}_{x} (x \in s) \text{ w.r.t. } μ|_s.$$$
Lean4
theorem _root_.Filter.EventuallyEq.restrict {f g : α → δ} {s : Set α} (hfg : f =ᵐ[μ] g) : f =ᵐ[μ.restrict s] g := by
-- note that we cannot use `ae_restrict_iff` since we do not require measurability
refine hfg.filter_mono ?_
rw [Measure.ae_le_iff_absolutelyContinuous]
exact absolutelyContinuous_restrict