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  "construction": "Open-boundary planar bivariate-bicycle code (Liang, Eberhardt, Chen, arXiv:2504.08887) with f = x + x^2 + y^2 and g = 1 + x^2 y + x^2 y^2 on a 8 x 8 grid (research/local2d/planar.py build_open_directional(8, 8), n = 128, k = 8), reduced to n = 108 by 20 restricted r=1 lattice grafts (arXiv:2504.08887 Sec. III E): a qubit lying in exactly one stabilizer of some type is removed together with that stabilizer, accepted only if k stays 8 and a NumPy RIS search screened at 600 fixed-seed trials and confirmed at 2500 fresh-seed trials finds nothing lighter than 6, followed by the weight-1 stabilizer cleanup of research/local2d/boundary_engine.py. Layout: a surviving qubit of unreduced index q = c*64 + i*8 + j sits at (i + j, j - i + c), one layer, spacing 1.",
  "origin": "submission",
  "date": "2026-09-20",
  "model": "Claude Fable 5.1",
  "notes": "Derived from the flagship planar family at L = (8,8) by r=1 grafting; not an independent construction. Fresh-seed RIS ladder on the saved code: 5000 trials -> 6, 20000 trials -> 6, 50000 trials -> 6. Claim: d <= 6, a witness-backed upper bound. Advances the weight-6 x local-2d-single board if the gate says so; novelty vs the literature unverified.",
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   "ris_trials_per_side": 1000000,
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   "tool": "research/kit search funnel, gf2_fast RIS"
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