← The blow-up search

A combined methodological note: four negative results from a computer-assisted-proof attempt that failed

Nothing here resolves the Clay problem. This is one long-shot programme's working record, published at the confidence its own gates recorded. What this is →

Route PUB1, leg 179, v1. DRAFT, for the user's review. This leg's landing does not approve it.

Status. This is the publication-scoping draft that leg 58's gate escalated to the user and that the strategic review recommended be bundled rather than shipped standalone. It is assembled entirely from banked results; nothing in it is new to the world, and its only contribution is arrangement. Every number is quoted from the JSON or journal of the leg that produced it: the provenance audit is writeup/novelty/leg_179.md, which lists each number against the file it was read from.

What this note is not. It is not a certificate, not a theorem about the Navier–Stokes equations, and not a claim that any link of this project's L1 → L4 chain has moved. None has, in 178 legs. The object throughout is the a = 0 Constantin–Lax–Majda (CLM) steady linearisation (an already-solved, already-published model) and every magnitude below bounds the difficulty of the real target from below, not above.


0. The shape of the argument, and why four results rather than one

A radii-polynomial / Newton–Kantorovich certificate needs four constants (Y₀, Z₀, Z₁, Z₂) and closure needs Z₁ < 1. Seven successive legs of this project tried to produce such a certificate for a 1D fluid transport model in a weighted ℓ¹ Fourier space, and did not. The useful residue is not the failure; it is that the failure has four separable causes, each of which was isolated, measured, and in two cases proved. Three of them are statements about method, not about this particular operator, and that is why they are worth writing down:

§ result kind where it bites
1 the exponent-sum conservation law a measured no-go over a family of spaces choosing the function space
2 the discrete-ball trap a soundness failure mode computing an induced norm
3 the A₂₁ inequality a theorem (two versions; the second supersedes the first) choosing the approximate inverse
4 the closure audit an exhaustion of a named enumeration deciding when to stop

They are ordered by where in a certificate construction a practitioner meets them.


1. The exponent-sum conservation law

The claim. In a weighted ℓ¹ Fourier space, a certificate for this operator needs two things of the weight, and they are separated by exactly one grading power, and the separation is conserved, so no choice of weights can satisfy both. The weights only decide which requirement pays.

The measurement. Write the domain weight exponent s, the codomain exponent t, and g = t − s. The two exponents are exact complements:

g −1.75 −1.0 −0.5 0.0 0.5 1.0 1.5
‖A_N‖_{Y→X} exponent in N 2.70 1.96 1.47 0.98 0.50 0.04 0.00
sharp quadratic S_K exponent in K 0.00 0.00 0.00 0.00 0.50 1.00 1.50
sum 2.70 1.96 1.47 0.98 1.00 1.04 1.50

So ‖A_N‖ ~ N^{1−g} and S_K ~ K^{g}. A certificate needs both exponents to be zero; their sum is ≥ 1 at every g and exactly 1 on 0 ≤ g ≤ 1. The measured minimum over the entire family is 0.98. In (s,t) coordinates a bounded inverse needs t ≥ s+1, a bounded quadratic needs t ≤ s, and the unit strip between them is empty. Both boundaries are pinned grid-independently by evaluating the exponents on the candidate lines: t = s−1 gives 1.96, t = s gives 0.98, t = s+1 gives 0.00–0.06.

The control, which is what makes it an attribution rather than a suspicion. Replace the transport factor (1 + cos θ) → 1 and change nothing else. The inverse boundary moves from t ≥ s+1 to t ≥ s−1: down by exactly two powers, which is the right number, because a non-degenerate first-order transport gains one power on inversion, this one loses one, and 1 + cos θ vanishes to order two at θ = ±π. The admissible regions then overlap on a full unit strip, the minimum exponent sum drops 0.98 → 0.00, and the overlap is non-empty at 9 of 9 values of s.

The obstruction is the far-field degeneracy of this specific operator: not the Newton–Kantorovich method and not the ℓ¹ framing. Remove the degeneracy and the same machinery has an admissible space pair immediately.

Why it is true, in one sentence. A diagonal weight on Fourier coefficients measures smoothness; the far-field transport needs decay; and these are not the same thing. The single mode cos kθ equals (−1)^k at θ = π: it does not decay at X = ∞ at all, for any k, and no diagonal weight can see that. Decay is a statement about the oscillatory-in-k structure of the coefficient sequence, i.e. about finitely many linear moment conditions. Asking a weighted-ℓ¹ pair to deliver both is a category error.

Novelty status, and the citation this note owes. Searched at primary source over four papers at full text plus a 39-item forward-citation sweep, and not found. The nearest published relative is Chen & Hou, Analytic finite-rank corrections for singularly weighted estimates (arXiv:2607.15256) §1.2, eqs (1.17)–(1.18), which publishes a weight tension of exactly this genre: one exponent squeezed from both sides, finite energy forcing β < 1 while the nonlocal term's constant diverges like (1−β)^{−1/2}. Three things differ, and any write-up must say so rather than pretend nothing like it is in print: it is in weighted L²/L^∞ energy spaces, not a weighted ℓ¹ sequence space; the competing requirements are damping vs. finite energy, not smoothness vs. far-field decay; and it is resolved by a choice (take α large) rather than stated as a no-go over a class of weights. The untested direction, stated as an explanation and not as a search result: the validated-numerics corpus that uses ℓ¹-Wiener norms with geometric weights ν > 1 avoids the algebraic-decay regime by construction, which is why nobody has had to state this.


2. The discrete-ball trap

The claim. Computing an induced operator norm by duality over the discrete unit ball is unsound. A discrete Hölder seminorm only inspects grid nodes, so the extremizer that duality selects is a grid-scale sign pattern whose interpolant has an enormous continuum norm. The resulting number is a true statement about a discrete object and a useless one about the continuum operator the certificate actually needs.

The magnitude, with a control that stays flat.

J (nodes) dual extremizer, inflation smooth control, inflation
125 2 994.16 1.0275
250 12 233.31 1.0273
500 49 698.93 1.0272

Inflation grows like J^{2.03} (fitted 2.0265): it is not a constant-factor nuisance, it diverges with refinement, so the trap gets worse the harder you work. The smooth control, computed through the same code path, is flat at ~1.027: the failure is a property of the extremizer, not of the norm evaluation.

What survives, and this is the constructive half. A two-point dual bound uses only inequalities the continuum norm implies, so it is valid. On the domain sup part it saturates in J (growth exponent +0.006): a genuinely uniform upper bound. On the domain seminorm part it is valid but lossy, growing like J^{+0.496}; it is reported with its growth so the slack is visible rather than hidden.

The practitioner's rule. Never let a rigorous step depend on node values alone. A coefficient representation determines a function on the whole domain; a grid does not.

Novelty status, and the background this note owes. Searched at primary source and not found. But the ambient mathematics is named and must be cited: the sampling-discretization literature (Kosov–Temlyakov and co-authors, arXiv:1812.08100, arXiv:2203.07126) asks exactly when a norm evaluated at finitely many nodes is comparable to the continuum norm, and its headline is that this degrades as the smoothness of the class drops. That is why the trap is true. None of those papers is about a dual/extremizer computation inside a certificate, none is about a Hölder seminorm on a graded grid, and none reports an inflation factor, so this is a concrete instance of a known phenomenon, and should be written as one, not as the discovery of one. Chen–Hou §1.4 states the same hygiene as working practice ("the numerical step only determines coefficients … the corrections are performed analytically on the resulting globally defined functions"), which again is the moral, not the claim.


3. The A₂₁ inequality, and the supersession, stated first

READ THIS BEFORE QUOTING ANYTHING IN THIS SECTION. This project banked two versions of this result. The first (leg 58) proves the inequality on the restricted class A₂₁ = 0. The second (leg 127) proves it for every bounded A, with A₂₁ completely free, by a different argument. The second supersedes the first. Leg 58's narrower statement is preserved below for the record and because its hypothesis-necessity control is still the sharpest one available, but the citable result is leg 127's, and any external presentation that cites the A₂₁ = 0 version is citing a weaker theorem than this project actually holds.

3.1 The current, correct form

Setting. L is the a = 0 CLM steady linearisation in the compactified odd-sine coefficient basis, bordered with the far-field amplitude as an extra unknown and its matching condition as an extra equation, in weighted ℓ¹ with w_k = (1+k)^s.

Hypotheses. s < 1; μ = 0 (no dissipation, so the tail block's diagonal is exactly zero and its far-field kernel lies in the space); and A a bounded operator on the space in the sense that it is the truncation of one fixed bounded operator, so ‖A‖_w is uniform in the truncation M. A₂₁, A₁₁, A₁₂, A₂₂ are all arbitrary.

Conclusion. Z₁ = ‖I − AL‖_w ≥ 1. Quantitatively, at truncation M, Z₁ ≥ 1 − ‖A‖_w · σ_min(L_M) with σ_min(L_M) = c_s M^{−(1−s)} → 0.

The two ingredients, and only one is this project's.

  1. Folklore, explicitly not claimed. ‖x‖ ≤ ‖(I−AL)x‖ + ‖A‖‖Lx‖ for every x, hence Z₁ ≥ 1 − ‖A‖σ_min(L). This is the contrapositive-with-remainder of the Z₁ < 1 ⟹ invertible hypothesis every radii-polynomial paper states.
  2. This project's content. That σ_min(L) = 0 on this operator in this space at s < 1, witnessed by an explicit sequence rather than found numerically.

The measurements.

quantity measured
fitted p in σ_min ∼ M^{−p} at s = 0 / 0.3 / 0.7 0.9925 / 0.6985 / 0.3202 (predicted 1 − s)
max deviation from 1 − s over s < 1, all K 0.0219
relative spread of σ_min over K = 2, 4, 8 for s < 1 0.29% (vs 2.14 at s = 1.5)
explicit witness vs numerical optimum ratio 1.0000000000045×, cosine 0.9999999999999998
rows of the finite block carrying the residual of Lv 1 (the truncation edge), with z_K = 0.0 exactly
the bound is attained: max slack at A = L⁻¹ 1.2366e−08
holds across leg 54's shape battery 196 / 196, min slack 7.7343e−10
μ > 0 control (the instrument can say otherwise) exponent ≤ 2.62e−03, i.e. σ_min saturates, vs 0.6985 at μ = 0

A mechanism worth recording, because the obvious repair is measured not to work. Bordering the operator with the far-field amplitude, the entire point of the assembled object, changes σ_min by 5.7e−15 relative at μ = 0. The reason is not that the singular sequence has no far-field-amplitude component: that component is 6.5–6.8% of ‖v‖₁ and growing with M. The reason is that its coupling column is supported on a single row, the truncation edge, so the border has nowhere else to reach. (The same two code arms differ by 6.1e−02 at μ = 0.1, so the comparison is live in both directions.)

The scope line, and it is the whole discipline of this section. Xu (arXiv:2607.19762) proves that the same operator, on origin-H², has point spectrum exactly {0,1} and essential spectrum meeting {Re λ ≥ −1/2} in the single line {Re λ = −1/2}, hence is invertible after modulation, with spectral gap 1/2. So this is a statement about the ℓ¹_w realization, never about the operator. No sentence anywhere in this project says the operator "has no bounded approximate inverse," and none may.

The nearest published relative, cited here on leg 183's recommendation. Xu §8 carries an interval-arithmetic no-go of its own (same operator, different realization, different certificate quantity, both concluding that an off-the-shelf enclosure does not enter) and leg 183 (which read §8 at full text and resolved whether it pre-empts this section: it does not) recommended that this scope line cite it alongside the origin-H² fact already above, in these terms:

Xu §8 rules out weighted resolvent enclosure of the raw grid truncation by norm-invariance of eigenvalues; §3 rules out bounded approximate inverses in ℓ¹_w by a norm-dependent lower-bound failure; the two are complementary and neither implies the other.

Leg 183 flagged this as an addition, not a correction to a claim (nothing in §3.1 above is altered by it) and recorded that a referee who knows the paper will ask. The differences that make the two statements complementary rather than nested are, in leg 183's own tabulation: Xu's object is the raw grid "without an origin condition" at a > 0, this section's is the bordered a = 0 matrix whose gauge row is Xu's own v′(0) origin functional; and Xu's quantity is exactly invariant under the relevant similarity as a theorem, whereas Z₁ is not, which is why §8's argument template does not transfer to Z₁.

3.2 The superseded form, kept for the record

Proposition NG (leg 58). On the class A_upper = {[[A₁₁, A₁₂], [0, A₂₂]]}, i.e. A₂₁ = 0, strictly larger than block-diagonal and containing the separately-measured gs_upper shape: Z₁ ≥ 1 + ‖A₁₁ B h‖_w/‖h‖_w ≥ 1, at every split K and every s < 1.

The proof is three lines: test I − AL on x = (0; h) where h is the tail block's kernel. Th = 0 kills the A₁₂ and A₂₂ terms, A₂₁ = 0 kills the third, the column is (−A₁₁Bh; h), and dividing by ‖h‖_w gives the bound. A₁₂ and A₂₂ never appear, which is exactly why the class is larger than block-diagonal, and exactly why the argument stops at A₂₁ ≠ 0.

Leg 58's own scope line, verbatim, and it is the sentence leg 127 retired: "MEASURED, NOT PROVED: every A with A₂₁ ≠ 0."

What survives supersession, and is still the sharpest thing in the section. Leg 58's hypothesis-necessity control. Hypothesis (H2) is that the tail block has a kernel in the space: Th = 0 with 0 < ‖h‖_w < ∞. The kernel is explicit from a two-term recursion; its measured decay exponent is −2.0024 (cokernel +1.0012), so it lies in ℓ¹_w exactly when s < 1: the crossing is measured at 1.0, reached from the opposite side to the Fredholm argument that first found it. And the control varies μ, which changes the tail operator itself: at μ = 0 the proposition forbids Z₁ < 1 and the measurement agrees at every K and in both weight classes; at μ = 0.1 the kernel is gone; by μ = 2.0 the same two in-class shapes reach Z₁ = 0.174027. The hypothesis is necessary, not decorative, and, as §5.2 shows, (H2) is also precisely where a later result found a corner the theorem does not reach.


4. The closure audit: when to stop, and how much of the difficulty was tuning

The question. The project's remaining stage proposed to search for a certificate over the function space, the operator split, and the constants. All three degrees of freedom were separately measured dead. Rather than run the search, the audit asks: enumerate that declared space, and does any admissible configuration remain that no banked measurement or theorem covers?

The answer: none. 1,686 configurations enumerated, 1,686 covered, 0 uncovered, by strongest coverage, 144 THEOREM / 1,032 STRUCTURAL / 510 MEASURED.

The accounting that the audit actually owes, and it is the interesting number. On decades of log₁₀ Z₁ from the block-diagonal baseline Z₁ = 10.458427:

decades share of the requirement
required (to reach Z₁ < 1) 1.019466 100%
delivered by tuning 0.067202 6.5919%
left unrealized (tuning headroom never searched) 0.171055 16.7789%
owned by structure 0.781209 76.6292%

The three shares sum to 1.0000000000000002, and the runner asserts it.

There was unexplored search space, and it would not have mattered. Tuning reached only 28.21% of its own ceiling, so the stage was not proposing to search an empty box. But a perfect search lands at Z₁ ≥ 6.0424, still 6.04× short of closure.

And on the proved class the accounting collapses. On A₂₁ = 0 the floor is the requirement: Z₁ ≥ 1 against a need for Z₁ < 1. Searchable headroom is exactly zero decades and structure owns 100%: as a theorem rather than as a battery. That is the sense in which "structure, not tuning" is theorem-grade here rather than merely measured.

Instrument checks, because an audit of banked numbers is only as good as its ability to reproduce them. Leg 54's two headline numbers, recomputed read-only through that leg's own landed code: block_diag 10.458427031841403 and ff_lift 8.959091169104095, relative gap 0.00e+00, bit-identical. The positive control reproduces leg 58's entire twelve-entry dial elementwise to 1.2482e−15.

Two things the audit's own controls caught, both of which are this project's standing lessons repeating. (1) The covering predicate was initially a tautology: run it on the dissipative μ > 0 operator, where a certificate demonstrably closes, and it answered "covered", because not one of the twelve clauses referenced μ. Scoping every clause to μ = 0 is what made the audit falsifiable. (2) The control's own realization was wrong first (it bordered the dissipative object with a far-field direction it does not have) giving a number off by 33,926×.

The limit on what this may be written as, and it is a hard limit. Automated certificate synthesis is published as sound but not complete (arXiv:2309.06090): a search that fails to find a certificate licenses no conclusion about the model. So the audit's claim is exhaustion of a named enumeration, this project's own declared search space, and never "no certificate exists." One flag from an earlier leg (a search-index concern) stands, untested by this work.


5. Two findings folded in as they landed, without softening or strengthening

5.1 Does the published record already account for the scaling exponent, and for a_c?

The two literature-anchored numbers this project carries had never been checked against the paper they came from. Reading Lushnikov–Silantyev–Siegel (arXiv:2010.01201) at full text settles both, and moves them in opposite directions.

(a) alpha(1/2) = 3: YES, explicitly and exactly. LSS Eq. (39), p. 11, is ξ = (x − x₀)/(t_c − t)^{1/3}, so their exponent is 1/3 and this project's alpha(1/2) = 3 follows from its own dictionary. It is on the page three further ways: the far-field exponent 1/α = 3 of Eq. (38), the closed form α₀(1/2) = 1/3 of Eq. (45), and Table 1 p. 48 listing α_e = 0.333333333 at a = 0.5. It is an exact closed-form solution LSS write down and prove.

Re-derived independently here: the PDE residual of their Theorem 2 is 7.92e−16 at a = 1/2, against a best of 6.05e−02 at a = 0.45 / 0.55 / 0, 13.9 decades apart. As the root of a scalar equation, p bisects to 0.333333333333333 and the exponent to 3.000000000000000; the same code path returns 1, 3, 6, 10 at other parameter values, so the 3 is a measurement of the object and not of the code.

The correction this produces, and it is a correction to a source count, not to a number. The three citations this project had been treating as independent confirmations are one ancestor, not three: three of the four authors of the secondary source are the three authors of LSS, LSS came first, and the third source's own text says its branch was checked against LSS's. Nothing claimed was wrong; the count of independent sources was inflated. The genuinely independent second discoverer is a different paper, J. Chen (arXiv:1908.09385), whom LSS themselves credit on p. 11.

(b) a_c ≈ 0.6890665: YES as primary source, NO from the exact solution. The value 0.6890665337007457… is LSS's own (abstract; §1 Eq. (8); §12), and this project's constant is that number truncated (relative offset 4.89e−08). But it is not implied by the exact a = 1/2 solution: LSS define it by α(a_c) = 0 and locate it numerically, while the exact family's closed form α₀(a) = 2(1−a)²/(2−a) is strictly positive for every a < 1 and has no root at all (scanned over a ∈ [−1, 0.999]; the scan's minimum is 2e−06 at the a → 1 end, so a root would have been seen). The useful new fact is about what kind of number it is: converged numerics from an iterative solve that does not converge past a_c at all, with the paper's own stated accuracy in that range being "at least 5 digits", not seventeen certified digits, whatever the printed tail looks like. Anyone quoting it should quote it as that.

5.2 A corner the closure audit does not cover: parked, and genuinely ambiguous

This is stated exactly as it landed. It is an open escalation, not a settled result: the branch that produced it was pushed and deliberately NOT merged, pending a human ruling.

What it is. On a compact support interval (available because the profile at 0 < a < 1 has compact support) a global Chebyshev basis is a fourth value of the audit's realization axis, which has three values on disk. The shape vocabulary this project uses enumerates no basis and no domain at all, so it can neither cover nor fail to cover it.

And the corner is two corners, which is the structural finding. One operator, two pairings that both close under it, opposite classifications:

domain → codomain unbounded part classified as
A (this project's own ansatz (1−v²)T_n → T_m bidiagonal, exactly zero diagonal, off-diagonal ~n/2 SHIFT
B) the Olver–Townsend airfoil pairing (arXiv:1507.00596) √(1−v²)U_{n−1} → T_m/√(1−v²) exact diag(−n) MULTIPLIER

The numbers, with their realization and gauge named. Realization B, A₂₁ = 0, bordered, N = 192, K = 16, amplitude gauge: block_diag 0.2737 and gs_upper 0.0874 at a = 0.8; 0.7370 and 0.2287 at a = 0.5, which is where the nonlinear constant Z₂ was previously measured finite. Z₁ moves 0.19% over an 8× refinement; the target is in its own space (margin −0.73); the operator is gated against direct pointwise evaluation at 3.4e−04; and the same code path returns 148.7 at the worst corner, so a value below 1 is a discrimination and not an instrument floor.

The caveat that must travel with every one of those numbers. Z₁ < 1 holds at 2 of 4 border gauges: the other two give 93.3 and 6.7e9. Over the whole parameter grid, 27 of 120 A₂₁ = 0 configurations fall below 1, all in realization B and none in realization A. A certificate designer does get to pick a gauge, so this is a restriction, not a refutation, but the headline is never stated as a bare Z₁.

Why this does not contradict §3. Every sub-1 number above has A₂₁ = 0, so it looks like a counterexample to Proposition NG. It is not. That proposition's hypothesis (H2) requires the tail block to have a kernel in the space, and realization B's tail is diag(−n), which has no kernel at any n ≥ 1. (H2) fails outright: the same way it fails for μ > 0 in leg 58's own dissipative control. The theorem is untouched; it simply does not reach this realization. That is exactly the sense in which the corner is new.

And the ambiguity, which this note states and does not resolve. The closure audit of §4 was performed on the a = 0 CLM linearisation, and this corner does not exist on that object at all: its measured decay exponent is −1.0000, the mass outside any radius never reaches zero, and a = 0 sits outside the range 0 < a < 1 on which the compact-support theorem holds. So "the audit's completeness claim is reversed" and "the audit's completeness claim was always scoped to an object where this corner is empty" are both defensible readings of the same measurements. Choosing between them is a human decision, and it has not been made. Anything published from §4 must carry §5.2 with it.

Its own ceiling. Z₁ is one of four constants and this is not a certificate: Y₀, Z₀, Z₂ were not measured here, and Z₂ was previously measured infinite on this same object in a different realization, with finiteness of the nonlinearity requiring a ≤ 1/2, which is why the a ≤ 0.5 values above are the ones that matter. Float64 throughout; no interval arithmetic. And the object is the gCLM profile on 0 < a < 1, not this project's nominal target.


6. Currency addenda: four things that landed after the bundle was specified

The bundle was specified before these landed. They are included because a scoping note that is out of date on its own record is the failure mode this note exists to prevent. Each is stated as its own leg banked it.

6.1 One of the three "dead realizations" must be de-rated twice over. An earlier leg recorded, for this note's attention, that of three dead realizations two (§1 and §2) are confirmed novel while the third (a weighted-energy formulation whose admissible window was measured to have width zero) is pre-empted in the published literature and must be de-rated to a statement about a trial-space choice. A later leg then sharpened that from "pre-empted" to "realization-dependent, and here is the other realization": the zero-width window is a property of the trial space (vanishing order p = 1), not of the operator. Hold the weight parameter at its published value and move p → 2 (the same degree of freedom, already measured elsewhere in this project's own record) and the admissible window goes from width 0.0 to 2.0, while the membership norm ratio per refinement goes from 1.6777e+07 (divergent) to 1.0000000000000002 (convergent). So the weighted-energy result is not publishable as a negative at all, and this note does not include it as one.

Two things follow for the other results. First, the organising concept (that an obstruction can belong to the realization rather than the operator) is published and named on this exact operator (Xu, Prop. 2 §3.1) and is used here, not claimed. Second, when that same classification is applied to the other banked negatives, the two that underpin §3 come back realization-invariant across every choice their own axes contain, and are besides subsumed by §3's own argument rather than being independent companions to it.

6.2 The "validated numerics cannot reach 3D" barrier is the field's, and its usual wording is wrong. Across a survey spanning fluid mechanics, parabolic blow-up, dispersive PDE, chemotaxis, pattern formation and the dynamical-systems computer-assisted-proof lineage, the largest number of spatial variables in any machine-certified singularity object is 2. Zero records satisfy all four clauses of the test. But one record certifies a genuinely 3D PDE object: van den Berg & Williams' Ohta–Kawasaki stationary states (SIAM J. Math. Anal. 51(1):131–158, 2019, giving the first existence proofs for the double gyroid and BCC-packed sphere solutions). The barrier is time-dependent singularity formation, not dimension, and the note states it that way. Every 3D singularity theorem carrying a computer-assisted ingredient obtains its 3D-ness from a symmetry reduction or from an ODE profile plus analysis. This matters for scoping because it means the 1D/2D restriction in §§1–4 is the field's scope, not a self-imposed limitation of this project.

6.3 The nearest competing modern technique's obstruction is technique-specific, not model-specific. A recent paper producing computer-assisted-proof-ready unstable self-similar singularities attributes its own precision floor to its training method, in its own words ("we are unable to reach maximum equation residuals much below 10⁻⁸"), and applied its precision-improving technique to only 4 of 12 solutions. The solutions left at the floor are the ones the technique was never applied to. So it exhibits an unapplied technique, not a model wall, which means §§1–4 should not be read as evidence that a different model class would have worked.

6.4 A Hilbert-space realization is scoped but not built, and the honest form of that matters here. A separate line found that origin-H² admits a structurally viable certificate formulation (a split, a shape, and no obstruction of §3's class) and it too was escalated and parked without building anything. What must not be written, and is not written here, is "the operator is invertible there, therefore a certificate is possible." Xu bounds his own result in his own abstract: the closed-form decay is obtained "on a weighted space of the conjugated variable reached from X by a bounded transfer map; we keep the two separate, since L₀ is non-normal and a spectral gap does not by itself give a decay rate in the X norm." A construction leg on that realization was in flight and had not landed when this note was drafted; nothing in this note is attributed to it.


7. Housekeeping: one stale framing note, corrected

A literature leg's novelty log describes a subsequent leg as "Route-NGX, live" and its subject as "the open A₂₁ ≠ 0 question this leg is mining literature for." That leg has since landed and closed the question; it is §3.1 above. The row is stale as written, and this note corrects it in place, in one sentence, explicitly as housekeeping. The literature leg's finding is untouched: every preconditioning construction in the papers it read still induces A₂₁ = 0, the one theorem that drops the nonzero-diagonal hypothesis still fails a different hypothesis (compact resolvent) on this operator, and a diagonal change of basis still cannot move a diagonal. Only the tense of the pointer changed.


8. What is claimable, and what is not

For anyone scoping this for external publication, the four results sit at three different grades and must not be levelled:

result grade what may be claimed
§3 the A₂₁ inequality theorem Z₁ ≥ 1 for every bounded A, on the ℓ¹_w realization at s < 1, on this operator. Not about the operator; not about the method in general. The inequality it rests on is folklore and is not claimed.
§1 exponent-sum conservation measured no-go over a family a conserved separation, minimum 0.98, with an ablation that attributes it to the operator's far-field degeneracy. Cite Chen–Hou §1.2 as the nearest published cousin and say what differs.
§2 discrete-ball trap soundness failure mode a concrete, quantified instance (~J^{2.03}) of a phenomenon whose ambient theory is published. Cite the sampling-discretization literature as background.
§4 closure audit exhaustion of a named enumeration 1,686/1,686 covered, and the tuning/structure split. Never "no certificate exists": synthesis is sound but not complete. And §5.2 must travel with it.

Three things this note must never be read as saying. (1) That the operator has no bounded approximate inverse: it is invertible on origin-H², published. (2) That the Newton–Kantorovich or radii-polynomial method is obstructed in general: §1's own ablation removes the obstruction by changing the operator. (3) That any of this bears on the target problem. The object is the a = 0 CLM linearisation, whose Y₀ is exactly zero for a degenerate reason (the anchor is one basis mode), so every magnitude here bounds the real target's difficulty from below.


9. Ceiling

The object throughout is the a = 0 CLM steady linearisation, except in §5.2 where it is the gCLM profile on 0 < a < 1. No dynamics were run. Nothing is claimed about this project's nominal target profile. Every number is float64 at a stated truncation; nothing here is interval-enclosed or rigorous in the computer-assisted-proof sense, including the two results called theorems, whose proofs are exact but whose verifying measurements are floating-point. No link of the L1 → L4 chain moved. None has moved in 178 legs. Clay odds remain ~0.05%.

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