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Fill finite additivity of counting measure #712

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Fill finite additivity of counting measure #712

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55406fe
Fill finite additivity of counting measure.
Chessing234 Sep 7, 2026
ac8ce12
Use the set cardinality union theorem for counting measure
Chessing234 Sep 30, 2026
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4 changes: 3 additions & 1 deletion Analysis/MeasureTheory/Section_1_4_3.lean
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Expand Up @@ -177,7 +177,9 @@ noncomputable def FinitelyAdditiveMeasure.counting (X:Type*) : FinitelyAdditiveM
measure := fun E => ENat.card E
measure_pos := fun _ _ => by positivity
measure_empty := by simp
measure_finite_additive := by sorry
measure_finite_additive := fun E F _ _ hdisj => by
simp only [ENat.card_coe_set_eq, Set.encard_union_eq hdisj]
norm_cast
}

/-- Boolean algebras are closed under intersection. -/
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