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This PR completes proofs for the PreL1 and L1 space structure in Section 1.3.4.

Summary of changes:

  • Complete proofs for PreL1 AddZeroClass and AddCommMonoid instances
  • Add ComplexAbsolutelyIntegrable.norm_zero helper lemma
  • Clean up comments in ComplexAbsolutelyIntegrable.zero proof
  • Complete proofs for L1 distance theorems (dist_eq and dist_eq_zero)

All proofs replace sorry placeholders with complete implementations, establishing the foundational structure for L¹ space as a normed vector space.

- Implement ComplexAbsolutelyIntegrable.zero: prove zero function is absolutely integrable using zero simple function representation and empty set measure
- Complete PreL1.inst_AddZeroClass.zero: use ComplexAbsolutelyIntegrable.zero instead of sorry
- Complete PreL1.inst_AddZeroClass.zero_add and add_zero: prove zero addition identities via function extensionality and Pi.zero_apply
- Complete PreL1.inst_addCommMonoid.add_assoc and add_comm: prove associativity and commutativity via function extensionality and ring properties

All proofs replace sorry placeholders with complete implementations.
Prove that the norm of the zero function is zero, completing the proof
that zero is absolutely integrable with norm zero.
- L1.dist_eq: Prove distance equals norm of difference (trivial by definition)
- L1.dist_eq_zero: Complete proof that distance is zero iff functions are equal almost everywhere

The proof shows that dist([f], [g]) = 0 ↔ f = g a.e. by:
1. Converting distance to integral of |f - g|
2. Using UnsignedLebesgueIntegral.eq_zero_aeZero
3. Showing the sets where functions differ are equal
@teorth teorth merged commit 7f41846 into teorth:main Jan 20, 2026
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2 participants