Hankel H₂(2) over Epicycloid S*_{3ℒ} · Geometric Function Atlas

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Certificate under review. This legacy or incomplete artifact is retained for audit, but cannot carry public proof wording until its v1 replay contract validates.

Stored legacy claim for Hankel H₂(2) over Epicycloid S*_{3ℒ}. Its proof wording is withheld pending a valid replayable v1 certificate.

What this rests on

The certificate reduces to these classical lemmas - each checkable by hand, independently of the engine.

1. Schur parametrisation is exact

The Schur recursion maps the closed polydisc \(\overline{\mathbb D}^{m}\) exactly onto the admissible coefficient vectors \((a_2,\dots,a_{m+1})\) of the class. Ranging the Schur parameters over \(\overline{\mathbb D}^{m}\) therefore sweeps every member's coefficients — nothing admissible is missed and nothing spurious is added.

Schur 1917; Foias–Frazho; Simon, OPUC. · schur-onto-coefficient-body
2. Rotation normalisation

The functional is weight-homogeneous under \(f(z)\mapsto e^{-i\theta}f(e^{i\theta}z)\), so its maximum is attained on the rotation-normalised slice \((\gamma_0\ge 0\) real\()\). This removes one real dimension and is verifiable by hand.

Elementary weight homogeneity. · rotation-reduction
3. Floating-point arithmetic is sound

Every float64 operation in the interval evaluation is widened by its IEEE-754 forward-error bound, so each computed interval rigorously encloses the true real value. The numerics are a certified enclosure, not a heuristic estimate.

IEEE-754 rounding; standard interval arithmetic. · ieee754-forward-error
4. The box partition is complete

Boxes are bisected at exactly representable midpoints, so the two children tile the parent with no gap and no overlap. The union of the certified leaf boxes is therefore provably the entire domain — coverage is exhaustive.

Exact dyadic subdivision. · bisection-partition

In the literature

This value over \(S^*(\varphi)\) is fixed by a published general theorem - Fekete–Szegő, \(|\gamma_2|\) and \(|A_3|\) by Ma & Minda (1994); the second Hankel determinant \(H_2(2)=(B_1/2)^2\) by Lee–Ravichandran–Supramaniam (2013). The registry re-certifies it mechanically - it is not a new result. See provenance & novelty.

dag engine m = 3 Schur params · 9,983 boxes · 4,992 certified leaves

Reproduce & raw certificate

Reproduce: python3 -m gft.proofs prove epicycloid_3 hankel2_2 "5/32" --slack 0.01
Recheck: python3 -m gft.proofs recheck data/proofs/epicycloid_3__hankel2_2.json

{
 "status": "PROVED",
 "engine": "dag",
 "statement": "max over S*(epicycloid_3) of |hankel2_2| <= 5/32 + 0.01",
 "class": "epicycloid_3",
 "functional": "hankel2_2",
 "bound": "5/32",
 "slack": 0.01,
 "target_sq_hex": "0x1.c4d6a161e4f75p-6",
 "m": 3,
 "vars": [
  "x0",
  "x1",
  "x2",
  "x3",
  "x4",
  "x5",
  "x6"
 ],
 "boxes_processed": 9983,
 "n_leaves": 4992,
 "terms": [],
 "evaluator": {
  "type": "factored-dag",
  "definition": "gft/dag.py (classical factored Schur formulas; symbolically verified against the expanded derivation in tests/test_proofs.py)",
  "code_commit": "see matching prove event in data/proofs/audit.jsonl"
 },
 "lemmas": [
  "schur-onto-coefficient-body",
  "rotation-reduction",
  "ieee754-forward-error",
  "bisection-partition"
 ],
 "failure": null,
 "leaves_parts": [
  "data/proofs/epicycloid_3__hankel2_2.w1.part0.npz",
  "data/proofs/epicycloid_3__hankel2_2.w3.part0.npz",
  "data/proofs/epicycloid_3__hankel2_2.w2.part0.npz",
  "data/proofs/epicycloid_3__hankel2_2.w0.part0.npz",
  "data/proofs/epicycloid_3__hankel2_2.final.npz"
 ],
 "sharp": {
  "class": "epicycloid_3",
  "functional": "hankel2_2",
  "bound": "5/32",
  "slack": 0.01,
  "bracket_lo": 0.140625,
  "bracket_hi": 0.16625,
  "extremal_gammas": [
   0.0,
   1.0,
   0.0
  ],
  "candidate": {
   "value_exact": "9/64",
   "value_float": 0.140625,
   "method": "attained extremal \u03c9=z\u00b2 (bracket_lo); moment-SOS-confirmed"
  },
  "exact": true,
  "note": "Candidate = the rigorously attained extremal value (sharp.bracket_lo, at \u03c9=z\u00b2), confirmed sharp by moment-SOS (gft/sos.py, cross-checked 3 ways) and equal to the general second-Hankel value (B\u2081/2)\u00b2 for S*(\u03c6) (Lee\u2013Ravichandran\u2013Supramaniam 2013). The earlier candidate equalled the loose B&B bound and exceeded (B\u2081/2)\u00b2 \u2014 impossible as a sharp value. Rigorous enclosure (bound/slack) unchanged; exact-rational upper certificate still open (heavy box)."
 }
}