T-013: Goebel's n=40 packing: seven verified first-order flexes, each refused at second order

V3 C3 rigidity confirmed

2026-08-30 established · Levy · n=40

Goebel's n=40 packing is infinitesimally flexible -- seven verified independent first-order flexes turn the sixteen-square tilted block -- and every retained flex is refused at second order by a verified non-negative self-stress, exactly over Q(sqrt 2), so no first-order argument can establish rigidity here.

Significance, composition and next rung
Significance
The first separation of infinitesimal from finite rigidity in this literature's cases: the sources assert rigidity without the distinction, and this refines rather than contradicts them.
Next rung
Characterise the admissible cone past dimension 45 (the corner-touching branch obstruction, D-391) or establish local rigidity by another route; the rigidity property stays undetermined until then.
Novelty
apparently-novel Not found in the recorded search, subject to its stated gaps

The case

Case record

n=40

6.716.828
678
6.3257.325
nn+1

Proven

6.71581≤s(40)≤6.828428

  • exact
  • rigid

Citation record n-040

lowerGuzhou0806 after wand125 et al. 2026, GitHub (confirmed T-145)

upperGöbel 1979, Squares in Squares

Open

  • optimality

The case record

LowerUpper
Gap22−541884199529≈ 0.11261137…

Results on the case

12 results in the register on n=40, 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    V0 C1 lower bound incomplete on this case, superseded by T-145

    Nagamochi · Nagamochi 2005 · source · register

  2. 2026-08-30 established T-013 this result

    Goebel's n=40 packing: seven verified first-order flexes, each refused at second order

    V3 C3 rigidity confirmed

    Levy · register

  3. 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; chelokot · Karakuş 2026 · chelokot Nagamochi counterexample 2026 · packet · register

  4. 2026-09-22 published T-044

    Weighted point lower bounds for ten counts in n=26…72, plus seven from the same files

    V3 C3 lower bound confirmed superseded by T-145

    wand125 after Levy, Stromquist, Nagamochi, Burns, Massaccesi · wand125 point bounds 2026 · packet · source · review · register

  5. 2026-09-27 published T-045

    Rectangle-density lower bounds replayed at 15 counts in n=18…78

    V3 C3 lower bound confirmed superseded by T-145

    wand125 after Tokoharu, Levy, Stromquist, Nagamochi, Burns, Massaccesi · wand125 rectangle bounds 2026 · packet · packet · source · review · register

  6. 2026-09-27 published T-046

    Rectangle-density lower bounds reported for 48 counts in n=18…95

    V0 C0 lower bound recorded superseded by T-145

    wand125 after Tokoharu, Levy, Stromquist, Nagamochi, Burns, Massaccesi · wand125 rectangle bounds 2026 · wand125 rectangle bounds 2026-09-28 · packet · packet · register

  7. 2026-09-29 published T-058

    Rectangle-certificate ceiling α·UB(n) proved for n=1..100; B·UB(n) on 64 grid rows

    V3 C3 method limit confirmed

    wand125 after Tokoharu, Daniel · wand125 tools 2026 · packet · register

  8. 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-145

    Karakuş · Karakuş 2026 · source · register

  9. 2026-10-01 published T-068

    Rectangle-density lower bounds verified at 34 counts in n=19…95

    V3 C3 lower bound confirmed on this case, superseded by T-145

    wand125 after Tokoharu, Levy, Stromquist, Nagamochi, Burns, Massaccesi · wand125 rectangle bounds 2026-10-01 · packet · source · review · register

  10. 2026-10-01 published T-074

    Rectangle-density lower bounds replayed at 31 counts in n=19…95

    V3 C3 lower bound confirmed on this case, superseded by T-145

    wand125 after Tokoharu, Levy, Stromquist, Nagamochi, Burns, Massaccesi · wand125 rectangle bounds 2026-10-01 · packet · packet · source · review · register

  11. 2026-10-10 published T-133

    s(40)>335427/50000=6.70854, by a clipped-corner transfer on a 401-direction net

    V3 C3 lower bound confirmed superseded by T-145

    Guzhou0806 after wand125, Tokoharu, Levy, Stromquist, Burns, Massaccesi · Guzhou0806 n40 clipped corner 2026-10-10 · packet · packet · source 1 · source 2 · review · register

  12. 2026-10-10 published T-145

    s(40)>1340000/199529=6.7158157…, by a continuous-pose interval kernel

    V3 C3 lower bound confirmed

    Guzhou0806 after wand125, Tokoharu, Levy, Stromquist, Burns, Massaccesi · Guzhou0806 n40 continuous pose 2026-10-10 · packet · packet · source 1 · source 2 · review · register