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Research notes on every problem, and a library of the papers behind them. Built from the open erdos repository.

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The lattice lemma in the certificate note can combine elements at very different scales: write z=qzg+ρzz=q_zg+\rho_z and require distinct 2-adic valuations of the nonzero residues, at most one zero residue, and ∑z∣ρz∣<g\sum_z|\rho_z|<g. The following observations, by Plasma AI and author-recorded, delimit a proposed averaging proof of this condition. They do not prove its existence for an arbitrary set.

Virtual points and repeated sources

Let g=z0/q0>0g=z_0/q_0>0, with q0q_0 odd, and use odd positive multipliers qzq_z for other elements. The virtual point vz=z/qzv_z=z/q_z satisfies

ρz=z−qzg=qz(vz−g),v2(ρz)=v2(vz−g).\rho_z=z-q_zg=q_z(v_z-g), \qquad v_2(\rho_z)=v_2(v_z-g).

Here v2v_2 is extended to nonzero rationals by subtracting the valuations of numerator and denominator. The lattice proof still works for rational gg: multiplying all residues and gg by a common denominator preserves the distinctness of their valuations and the strict budget. A companion's cost is qz∣vz−g∣q_z|v_z-g|, so different sources carry different weights.

Under the strict total budget, a selected collection cannot use two different representations of the same element zz. Indeed, if the multipliers are p≠qp\ne q, then

∣z−pg∣+∣z−qg∣≥∣p−q∣g≥g.|z-pg|+|z-qg|\ge |p-q|g\ge g.

For two odd multipliers the lower bound is 2g2g. Thus repeated-source exclusion is automatic for this strict-budget construction. The statement does not cover relaxed graded budgets whose total may exceed gg.

The real center can also be chosen independently of the virtual pivot. Let vi=zi/qiv_i=z_i/q_i for positive odd integers qiq_i, and suppose the nonzero differences vi−v0v_i-v_0, 1≤i≤k1\le i\le k, have distinct 2-adic valuations. If some real c>0c>0 satisfies

∑i=0k∣zi−qic∣<c,(F)\sum_{i=0}^k |z_i-q_ic|<c, \tag{F}

then {z0,…,zk}\{z_0,\ldots,z_k\} is dissociated. Repeated sources are excluded by the same strict-budget argument. In a ternary relation write Q=∑iεiqiQ=\sum_i\varepsilon_iq_i. If Q≠0Q\ne0, rewriting around cc contradicts (F). If Q=0Q=0, rewriting around v0v_0 gives ∑i≥1εiqi(vi−v0)=0\sum_{i\ge1}\varepsilon_iq_i(v_i-v_0)=0; the least valuation is unique since every qiq_i is odd. All these coefficients vanish, and Q=0Q=0 then forces the remaining coefficient to vanish. This is a weighted version of the free-center lemma. Its averaging problem is still open, but the center need not be constrained to one of the virtual points.

A generic weighted packing inequality is false

Let TT be a full binary tree whose leaves are labeled by a finite set of intervals Ii=[xi−ri,xi+ri]I_i=[x_i-r_i,x_i+r_i] in [0,1][0,1]. Set Si={j:xi∈Ij}S_i=\{j:x_i\in I_j\}, which contains ii. Let mim_i be the depth of leaf ii in the tree induced on SiS_i, after vertices with just one child are suppressed. There is no absolute constant KK such that

∑iri2−mi≤K(W)\sum_i r_i2^{-m_i}\le K \tag{W}

for every such interval family and binary tree.

Here is an explicit family with linear growth in the number of scales. For an integer H≥0H\ge0 and each s=0,…,Hs=0,\ldots,H, take the 2s2^s dyadic cell centers and radii

xs,j=2j+12s+1,rs,j=2−s−2,0≤j<2s.x_{s,j}=\frac{2j+1}{2^{s+1}},\qquad r_{s,j}=2^{-s-2},\qquad 0\le j<2^s.

The centers are pairwise distinct and each interval lies strictly inside its cell. At a center of level ss, no interval of a finer level can contain that center: it is a cell boundary at every finer level. No other interval of level ss contains it either. Thus Ss,jS_{s,j} consists of (s,j)(s,j) itself and labels of coarser levels.

Let BsB_s be any full binary tree on the level-ss labels. Put T0=B0T_0=B_0 and recursively make TsT_s the tree with children Ts−1T_{s-1} and BsB_s. Use THT_H as the tree on all labels. In its restriction to Ss,jS_{s,j}, all finer levels disappear, and (s,j)(s,j) is the sole surviving leaf of BsB_s. Every other surviving leaf is in Ts−1T_{s-1}. Therefore its induced depth ms,jm_{s,j} is either zero or one, and

∑iri2−mi≥12∑s=0H2s2−s−2=H+18.\sum_i r_i2^{-m_i} \ge \frac12\sum_{s=0}^H2^s2^{-s-2} =\frac{H+1}{8}.

This is unbounded, proving the failure of (W). The construction is explicit for every HH and has no computational premise.

What remains for folding

The virtual points of a fixed source zz are not arbitrary interval centers: as the odd multiplier varies, they form the specific family z/qz/q, and a threshold on weighted distance gives intervals of radius proportional to 1/q1/q. The obstruction above does not assert that its interval family has this form with the required arithmetic relations. Consequently it refutes a proof using arbitrary weighted intervals and only the Kraft equality, not the folding route itself.

A successful averaging argument must use the compatibility of the different multipliers of each source, or another arithmetic property absent from (W), to produce a modulus with sufficiently many cheap residues at distinct levels. This is the unresolved interface in the constant-loss route.