T-216: Mixed rectangle-measure lower bound s(108)≥531/50 verified, on the 201-direction net

V3 C3 Lower bound confirmed

2026-10-16 published · Hosono after Tokoharu and Levy · n=108

A rectangle measure of wand125/square-packing, published on 16 October 2026 and reported in jlevy/squares#446, proves s(108)≥531/50 = 10.62.

The certificate, mixed_n108_L1062, is a density of 823 uniform rectangles in D4 orbits, and no point mass, of total mass 10799999/100000 < 108. Its declared net has 201 half-angle tangents of step 83/40000 at core side 9977/10000. Since 9977/10000 (1 + 83/40000) = 399908091/400000000 < 1, and the last tangent 83/200 is past tan(pi/8), every unit square contains a closed concentric core at a net angle strictly inside its interior. The search started from a published certificate at a smaller count, mapped to this side and re-solved by linear programming; lifting describes the search, not a premise of the proof.

The maintained sqverify-fast census decided the retained candidate at all 201 directions, with summary VERIFIED and return code 0. Its whole-net control receipt records CONTROLS_REFUSED: the 99/100 mass mutant is refused at every direction, and the near-threshold mutant is refused at the least-bound leaf. The exact premise and saved-point audit recomputed all 201 refusal witnesses and their original captures. Two separately prompted mathematical reviews accepted the certificate's implication and exact premises; the second used the strongest tier at maximum reasoning required by the import runbook. The audits read the retained complete replay; they did not rerun the native engine.

The verified lower lane rises from 10.4121138007... (Karakuş's strip bound, T-083 and T-084) to 10.62, and the reported lane from T-180's closed form, 10.484093855851..., to the same value. The bound is confirmed by a re-implementation sharing the producer's components. The producer's sqverify-proof-net is a copy of this repository's sqverify_fast crate with its declared-net reader changed, so agreement supplies no independent full implementation or second method and establishes no optimality.

wand125 after Tokoharu and Levy, square-packing. The source reports AI assistance under human direction.

Significance, composition and next rung
Significance
The strongest verified and reported lower bound on record at n=108, 0.1359 above the previous reported lane and 0.2079 above the verified lane, by the certificate kind and standard net of T-082, T-090 and T-091, with no new technique, at S3 as T-176 to T-178 are.
Composition
One primary certificate on its source-report and maintained-replay entries. The full replay uses sqverify-fast at all 201 directions of the retained candidate's declared net: one interval-certified method, sharing the producer's sqverify_fast components, C3. The separate standard-library audits check exact premises and saved poses; neither decides coverage between those poses, supplies an independent full implementation, or adds a second method.
Next rung
V4 and C4 require a human oversight record alongside the two retained adversarial AI reviews. A full implementation that shares no producer code would add independent full confirmation; the exact point audits do not provide that. The other 17 fine-net imports remain under think-f40c.
Novelty
previously-published Present in an identified source

The case

Case record

n=108

10.6210.905
101112
10.39211.392
nn+1

Proven

10.62000≤s(108)≤10.904822

  • exact

Citation record n-108

lowerHosono after Tokoharu and Levy 2026, GitHub (confirmed T-216)

upperXu et al., GitHub (confirmed T-174)

Open

  • optimality

The case record

LowerUpper
Gap0.28482101…

Results on the case

13 results in the register on n=108, oldest first, each with what it established and how it stands now.

  1. 2005 published T-007

    s(n)≥min(⌈n⌉,n−2⌊n⌋+1+1) for 4≤n≤324

    V0 C1 Lower bound incomplete on this case, superseded by T-216

    Nagamochi · Nagamochi 2005 · source · register

  2. 2026-09-04 published T-085

    Nagamochi 2005, Lemma 1 is false for every container with a>3 and b>2

    V3 C3 Correction confirmed

    Karakuş; Vlasenko · Karakuş 2026 · chelokot Nagamochi counterexample 2026 · packet · register

  3. 2026-09-29 published T-083

    s(n)≥1/2+n−⌊n⌋+1/4 for every nonsquare 8≤n≤324

    V3 C3 Lower bound confirmed on this case, superseded by T-216

    Karakuş · Karakuş 2026 · source · register

  4. 2026-10-05 published T-101

    Exact certificates of 77 catalogue packings: s(n) ≤ S', 1.2e-16 to 9.8e-15 above each side

    V3 C3 Upper bound confirmed on this case, superseded by T-174

    Daniel after Couzo, de Winter, Ellsworth, Levy · evand exact optima 2026-10-05 · packet · register

  5. 2026-10-07 published T-113

    s(n)≤Sn at ten counts, n=108 to 303, from new SQUISH rational packings

    V3 C3 Upper bound confirmed superseded by T-174

    Chaoweeraprasit after Ellsworth · SQUISH ten packings 2026-10-07 · packet · register

  6. 2026-10-07 published T-116

    s(n)≤Sn at nine counts, from the second SQUISH update’s new rational packings

    V3 C3 Upper bound confirmed superseded by T-174

    Chaoweeraprasit after Ellsworth, Couzo and SQUISH · SQUISH second update 2026-10-07 · packet · register

  7. 2026-10-08 published T-125

    Complete rational construction reports at 25 counts

    V3 C3 Upper bound confirmed superseded by T-174

    Xu · ry-xu square packing 2026 · packet · register

  8. 2026-10-08 published T-127

    Fourteen rational refinements, seventeen complete source cases

    V3 C3 Upper bound confirmed on this case, superseded by T-174

    Gupta after Chaoweeraprasit, Daniel · Gupta rational refinements 2026-10-08 · packet · register

  9. 2026-10-08 published T-128

    Eight complete rational refinements from Couzo

    V3 C3 Upper bound confirmed superseded by T-174

    Couzo after Xu, Chaoweeraprasit, Gupta, Ellsworth, Daniel, Levy · Couzo exact refinements 2026-10-08 · packet · register

  10. 2026-10-09 published T-138

    Exact witnesses at Mishapolk's printed ceilings, the smallest known at 103 and 258 when registered

    V3 C3 Upper bound confirmed superseded by T-174

    Polkovskyi after Stenlund, Friedman, Ellsworth, Chaoweeraprasit, Couzo, Xu, Levy · Mishapolk decimal poses 2026-10-09 · packet · register

  11. 2026-10-13 published T-174

    Tighter certificates at 68 counts from PingYou Ltd, of others' packings and its own

    V3 C3 Upper bound confirmed

    PingYou Ltd after Friedman, Ellsworth, Daniel, Xu, Barnett, Couzo, Ostashev, Chaoweeraprasit, Gupta, Fang, Polkovskyi, Levy · PingYou PR 574 certificates 2026-10-13 · packet · register

  12. 2026-10-13 published T-180

    Closed-form lower bound s(N)≥a(N) for every non-square N≥49, reported

    V0 C1 Lower bound reviewed on this case, superseded by T-216

    Hosono · wand125 closed form 2026-10-14 · packet · packet · register

  13. 2026-10-16 published T-216 this result

    Mixed rectangle-measure lower bound s(108)≥531/50 verified, on the 201-direction net

    V3 C3 Lower bound confirmed

    Hosono after Tokoharu and Levy · wand125 fine-net lower bounds 2026-10-16 · packet · source · review · register