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docs: M3c/M1/M4 scope — the operator bridge + Mathlib-gap survey - #13

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Scopes the remaining operator-level bridge in docs/INDEX_PAIRING.md, now that the function-theoretic count (M3a dim ker = k, M3b coker = 0) is on main.

Key finding from a Mathlib survey — the operator index = k has a real gap on every route:

  • M1 (weighted L²(L_k) sections + twisted ∂̄): build from scratch (no line-bundle L² in Mathlib).
  • Route A — Weyl's lemma / elliptic regularity for ∂̄: fully absent in Mathlib → blocked.
  • Route B — Landau/Hermite decomposition (recommended): L²(L_k) ≅ ⨁ₙ ℂᵏ via Hermite-Gaussian eigenfunctions ⇒ D⁺ ≅ magneticDirac k, transporting the formalized model index = k. Gap: Mathlib has only Hermite polynomials + Rodrigues, not the L²(ℝ) orthonormal basis.
  • Jon's WIP: Fredholm operators for the index pairing (Riesz–Schauder in progress) #11 (merged): Riesz–Schauder gives Fredholm well-definedness of index(D⁺); the value = k still needs Route B.

Recommended first step: build the Hermite orthonormal basis of L²(ℝ) — the gating lemma for Route B, a clean reusable Mathlib-gap fill. (Even so, M1 + the magnetic guiding-center reduction remain substantial — this is a multi-step analytic build.)

Doc-only. Refreshes the Mathlib inventory.

🤖 Generated with Claude Code

…rvey

Now that the function-theoretic count is done (M3a/M3b on main), scopes the remaining
operator-level bridge in docs/INDEX_PAIRING.md:

- M1: build the weighted L²(L_k) sections + the twisted ∂̄ operator (from scratch; no
  line-bundle L² in Mathlib).
- Route A (Weyl's lemma / elliptic regularity for ∂̄): fully absent in Mathlib — blocked.
- Route B (Landau/Hermite decomposition, recommended): L²(L_k) ≅ ⊕ₙ ℂᵏ via Hermite-Gaussian
  eigenfunctions, D⁺ = lowering, ker = ℂᵏ, ≅ magneticDirac k (transports the formalized model
  index = k). Gap: Mathlib has only Hermite polynomials + Rodrigues, NOT the L²(ℝ) orthonormal
  basis — building that basis is the gating, reusable first step.
- Connection to Jon's merged Riesz–Schauder (#11): gives Fredholm well-definedness of index(D⁺);
  the value = k still needs Route B.
- Recommended first step: the Hermite L²(ℝ) orthonormal basis.

Refreshed the Mathlib inventory (count done; Hermite-basis / Weyl / line-bundle-L² gaps).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
@JonBannon
JonBannon merged commit 4947440 into main Jun 20, 2026
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