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Fill countable additivity of restriction to a sub-sigma-algebra #708

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Fill countable additivity of restriction to a sub-sigma-algebra #708

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3 changes: 2 additions & 1 deletion Analysis/MeasureTheory/Section_1_4_3.lean
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Expand Up @@ -175,7 +175,8 @@ theorem FinitelyAdditiveMeasure.isCountablyAdditive_restrict_alg {X:Type*} {B B'
def CountablyAdditiveMeasure.restrict_alg {X:Type*} {B B': ConcreteSigmaAlgebra X} (μ: CountablyAdditiveMeasure B) (hBB' : B' ≤ B) : CountablyAdditiveMeasure B' :=
{
toFinitelyAdditiveMeasure := μ.toFinitelyAdditiveMeasure.restrict_alg hBB',
measure_countable_additive := by sorry
measure_countable_additive := fun E hE hdisj =>
μ.measure_countable_additive E (fun n => hBB' (E n) (hE n)) hdisj
}

/-- Example 1.4.29 (Dirac measure) -/
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