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 "name": "[[84,2,?]] weight-4 multivariate-bicycle finalist 5, 2D-local bilayer layout",
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 "provenance": {
  "authors": [
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  "construction": "Two-term multivariate bicycle on Z_7 x Z_6; A=[[0, 0], [4, 4]], B=[[0, 0], [5, 5]]; identity-normalized x/y/xy supports; screen seed=20260816, sample=4.",
  "references": [
   "arXiv:2406.19151"
  ],
  "date": "2026-08-16",
  "notes": "Screened at 160 trials; package witness search used 1600 trials. Distance is an upper bound. LAYOUT added 2026-08-20: a 1-layer planar layout with measured interaction radius 6.4031 (integer-grid sites, min site spacing 1.0, at most 1 qubits per site), placing the code in the local-2d-bilayer class with geometric efficiency g = 0.0046. Layout credit and method are recorded in locality.contributed_by; the code, its distance claims, and its authorship are unchanged. Part of the layout-filling effort (issue #654 discussion)."
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   "date": "2026-08-20",
   "method": "Tier-0/1 pipeline: spectral (Laplacian eigenvector) initialization snapped to an integer grid, then simulated annealing over site assignments (single-qubit relocations + pair swaps, max-diameter objective, 2 seeds per layer option). Search driven by Claude Fable 5."
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  "rounds": 9,
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  "notes": "Generic sequential two-block extraction: one ancilla per check, X checks then Z checks each round with joint reset/measure layers; CX layers are a proper edge coloring of each Tanner graph (4 X + 4 Z CX layers per round, schedule seed 0; hook-aware orders: every CNOT order suffix needs >= d-1 further data errors to complete a logical, layered by min-conflicts search). Screened by RIS on ker(H_dem) and an observable-constrained seeded BP+OSD search; witnesses validated in GF(2).",
  "contributed_by": {
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   "date": "2026-09-18",
   "method": "generic CSS memory schedule: one ancilla per check, CX layers from a bipartite edge coloring, CNOT orders filtered by a hook-error criterion; screened by RIS on ker(H_dem) and an observable-constrained seeded BP+OSD search"
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}