English
If f is strongly measurable with respect to a filter, then refining the filter preserves strong measurability along the same measure.
Русский
Если функция сильно измерима относительно фильтра, то уточнение фильтра сохраняет сильную измеримость по той же мере.
LaTeX
$$$ \text{StronglyMeasurableAtFilter}(f,l',\mu) \Leftarrow \text{StronglyMeasurableAtFilter}(f,l,\mu) \text{ when } l' \le l $$$
Lean4
protected theorem eventually (h : StronglyMeasurableAtFilter f l μ) :
∀ᶠ s in l.smallSets, AEStronglyMeasurable f (μ.restrict s) :=
(eventually_smallSets' fun _ _ => AEStronglyMeasurable.mono_set).2 h