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Summary

This PR completes the formalization of Remark 1.3.10 and adds absolute integrability results:

Bug fix:

  • Fix CantorInterval exponent from (n+1) to n in Section_1_2_2

Remark 1.3.10 completion:

  • Complete proof showing inverse image of measurable set need not be measurable
  • Add DyadicRationals definition with countability proof
  • Refactor binary-to-ternary function implementation with clearer naming (f_lifted)
  • Move helper lemmas (geometric series, floor operations) for better organization
  • Remove unused BinaryToTernaryProperties structure

Updates on Jan12:

  • Complete RealMeasurable.iff and ComplexMeasurable.iff proofs: prove equivalence between RealMeasurable and ComplexMeasurable for real functions, and between ComplexMeasurable and measurability of real/imaginary parts
  • Complete ComplexAbsolutelyIntegrable.abs and RealAbsolutelyIntegrable.abs proofs: prove absolute value of absolutely integrable functions is unsigned absolutely integrable
  • Complete absolute integrability equivalence proofs: prove RealAbsolutelyIntegrable ↔ ComplexAbsolutelyIntegrable for real functions, ComplexAbsolutelyIntegrable.re/im showing parts are absolutely integrable, and ComplexAbsolutelyIntegrable ↔ both parts absolutely integrable using triangle inequality

Files changed: Section_1_2_2.lean, Section_1_3_2.lean, Section_1_3_4.lean

- Section_1_2_2: Fix CantorInterval exponent from (n+1) to n
- Section_1_3_2: Refactor Remark 1.3.10 with simplified strategy docs, add DyadicRationals definition and countability proof, clarify implementation differences from textbook, update BinaryToTernaryProperties structure
- Relax binaryDigit_partial_sum_lt signature (remove Ico constraint), update call sites
- Fix sum_add_tsum_nat_add calls to use Summable.sum_add_tsum_nat_add
- Complete Remark 1.3.10 example proof: show A' measurable via complement of countable set, then F' = f⁻¹(E) ∩ A' is measurable intersection
- Rename f to f_lifted and update related lemma names for clarity
- Use underscore prefix for unused hypothesis names
- Move geometric series and floor helper lemmas (tsum_two_thirds_geometric, tsum_tail_bound, floor_two_mul_odd_ge, floor_two_mul_even_le, floor_two_mul_eq_of_mod_eq) before Remark_1_3_10 namespace
- Remove BinaryToTernaryProperties structure and binaryToTernaryFn definition (unused)
- Simplify DyadicRationals comment
- Clean up proof structure and organization
- Complete RealMeasurable.iff: prove equivalence between RealMeasurable and ComplexMeasurable for real functions using simple function approximations and continuity
- Complete ComplexMeasurable.iff: prove equivalence between ComplexMeasurable and RealMeasurable for real/imaginary parts, constructing complex simple functions from real ones
….abs proofs

- Complete ComplexAbsolutelyIntegrable.abs: prove that absolute value of complex absolutely integrable function is unsigned absolutely integrable, using measurability and continuity of norm
- Complete RealAbsolutelyIntegrable.abs: prove that absolute value of real absolutely integrable function is unsigned absolutely integrable, using same approach with real norm
- Complete RealAbsolutelyIntegrable.iff: prove equivalence with ComplexAbsolutelyIntegrable for real functions using norm equality
- Complete ComplexAbsolutelyIntegrable.re/im: prove real/imaginary parts of complex absolutely integrable functions are real absolutely integrable, using measurability and integral monotonicity
- Complete ComplexAbsolutelyIntegrable.iff: prove equivalence with both parts being absolutely integrable, using triangle inequality bound |f| ≤ |Re(f)| + |Im(f)| and integral additivity
@teorth teorth merged commit b42731f into teorth:main Jan 14, 2026
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