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Fill the finitely additive measure calculus in Exercise 1.4.20 - #718

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Fill the finitely additive measure calculus in Exercise 1.4.20#718
Chessing234 wants to merge 6 commits into
teorth:mainfrom
Chessing234:feat/fam-mono-additivity

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Summary

  • Boolean algebras are closed under intersection, difference, and finite unions, from complement and binary union.
  • Finitely additive measures are monotone, finitely additive, finitely subadditive, and satisfy μ(E ∪ F) + μ(E ∩ F) = μ(E) + μ(F).

Test plan

  • lake build Analysis.MeasureTheory.Section_1_4_3; CI covers the module.

Made with Cursor

…e, and finite unions.

These are the set operations used in the finitely additive calculus.
A measurable subset splits off a nonnegative remainder, so its measure cannot exceed the larger set.
Disjoint finite unions reduce to binary additivity by induction on the index set.
The union is at most the sum of the pieces after splitting off a disjoint remainder.
… measures.

Both sides split along the disjoint remainder F \\ E.
Additivity on EReal is left-biased, so the comparison has to add the same first summand on both sides.
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