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The sequence WWW, three sumfree classes covering W^\hat WW^, and four sumfree sets covering Z7×Z7∖{0}\mathbb{Z}_7 \times \mathbb{Z}_7 \setminus \{0\}Z7​×Z7​∖{0}

Definition
ClassicalSchurValues

by mysticflounder · Sep 26, 2026 · Mathlib 0df444a (Lean v4.33.1)

additive-combinatoricscombinatoricsramsey-theoryschur-degree-block-sumssum-free-sets

This bundle records the explicit finite objects of the note from which the lower bounds L(4)≥16L(4) \ge 16L(4)≥16 and L(5)≥49L(5) \ge 49L(5)≥49 are obtained.

  1. The sequence WWW (Lean seqW) of length 151515 and sum 313131, displayed below (note, §2).
  2. Three finite sets of positive integers (Lean classesW, indexed by 0,1,20, 1, 20,1,2; note, Lemma 2): C0={1,3,8,12,18,22,28}C_0 = \{1, 3, 8, 12, 18, 22, 28\}C0​={1,3,8,12,18,22,28}, C1={2,6,7,10,11,25,26,29,30}C_1 = \{2, 6, 7, 10, 11, 25, 26, 29, 30\}C1​={2,6,7,10,11,25,26,29,30} and C2={9,13,16,17,19,20,21,27,31}C_2 = \{9, 13, 16, 17, 19, 20, 21, 27, 31\}C2​={9,13,16,17,19,20,21,27,31}.
  3. Four subsets D0,D1,D2,D3D_0, D_1, D_2, D_3D0​,D1​,D2​,D3​ of Z7×Z7\mathbb{Z}_7 \times \mathbb{Z}_7Z7​×Z7​ (Lean partitionZ7Z7, indexed by 0,1,2,30, 1, 2, 30,1,2,3; called C0,…,C3C_0, \dots, C_3C0​,…,C3​ in Theorem 5 of the note), each with 121212 elements, listed in the table.
setelements (a,b)∈Z7×Z7(a, b) \in \mathbb{Z}_7 \times \mathbb{Z}_7(a,b)∈Z7​×Z7​
D0D_0D0​(0,2) (0,5) (1,4) (2,3) (2,4) (3,2) (3,3) (4,4) (4,5) (5,3) (5,4) (6,3)
D1D_1D1​(1,1) (1,3) (1,5) (1,6) (3,0) (3,5) (4,0) (4,2) (6,1) (6,2) (6,4) (6,6)
D2D_2D2​(0,3) (0,4) (1,0) (1,2) (2,1) (2,6) (3,4) (4,3) (5,1) (5,6) (6,0) (6,5)
D3D_3D3​(0,1) (0,6) (2,0) (2,2) (2,5) (3,1) (3,6) (4,1) (4,6) (5,0) (5,2) (5,5)

The sequence WWW and, by Lemma 1 of the note, its set of block sums are

W=(1,1,1,6,1,1,1,7,1,1,1,6,1,1,1),W^=[1,3]∪[6,13]∪[16,22]∪[25,31],W = (1, 1, 1, 6, 1, 1, 1, 7, 1, 1, 1, 6, 1, 1, 1), \qquad \hat W = [1, 3] \cup [6, 13] \cup [16, 22] \cup [25, 31],W=(1,1,1,6,1,1,1,7,1,1,1,6,1,1,1),W^=[1,3]∪[6,13]∪[16,22]∪[25,31],

where [a,b]={a,a+1,…,b}[a, b] = \{a, a+1, \dots, b\}[a,b]={a,a+1,…,b}; so W^\hat WW^ has 252525 elements. In the note, C0,C1,C2C_0, C_1, C_2C0​,C1​,C2​ are sumfree and partition W^\hat WW^ (Lemma 2), so sdeg⁡(W^)≤3\operatorname{sdeg}(\hat W) \le 3sdeg(W^)≤3; and D0,…,D3D_0, \dots, D_3D0​,…,D3​ are sumfree in Z7×Z7\mathbb{Z}_7 \times \mathbb{Z}_7Z7​×Z7​ and partition its 484848 nonzero elements (Theorem 5).

The sequence WWW with the classes C0,C1,C2C_0, C_1, C_2C0​,C1​,C2​ is the witness for L(4)≥16L(4) \ge 16L(4)≥16. The four sets DiD_iDi​, through the lift of the Lift bundle, give L(5)≥49L(5) \ge 49L(5)≥49.

Formalization Note The classes are Lean Finsets indexed by Fin 3 and Fin 4. The bundle contains only the data. The facts that the mission uses (the sumfree property of C0,C1,C2C_0, C_1, C_2C0​,C1​,C2​ and their cover of W^\hat WW^, the bound 4L4L4L on the sum of the first LLL entries of WWW for L≤15L \le 15L≤15, and the sumfree property of the DiD_iDi​ in the group and their cover of the nonzero elements) are proved inside the proofs of the theorems that use them. The disjointness of the classes, which the note also states, is not needed there.

Definition code
-- Generated from lean/ClassicalSchur/Values.lean by skeleton
-- subtraction: every declaration except the def-material below is deleted,
-- and project imports are rewritten to their platform Definitions bundles.
import Mathlib

namespace ClassicalSchur



/-- The sequence `W` of the note: length 15, sum 31. -/
def seqW : List ℕ := [1, 1, 1, 6, 1, 1, 1, 7, 1, 1, 1, 6, 1, 1, 1]

/-- The classes `C₀, C₁, C₂` of Lemma 2 of the note. -/
def classesW : Fin 3 → Finset ℕ :=
  ![{1, 3, 8, 12, 18, 22, 28}, {2, 6, 7, 10, 11, 25, 26, 29, 30},
    {9, 13, 16, 17, 19, 20, 21, 27, 31}]

/-- The four sets of Theorem 5 of the note: a partition of the nonzero
elements of `ℤ₇ × ℤ₇` into sets that are sumfree in the group. -/
def partitionZ7Z7 : Fin 4 → Finset (ZMod 7 × ZMod 7) :=
  ![{(0, 2), (0, 5), (1, 4), (2, 3), (2, 4), (3, 2), (3, 3), (4, 4), (4, 5), (5, 3), (5, 4),
      (6, 3)},
    {(1, 1), (1, 3), (1, 5), (1, 6), (3, 0), (3, 5), (4, 0), (4, 2), (6, 1), (6, 2), (6, 4),
      (6, 6)},
    {(0, 3), (0, 4), (1, 0), (1, 2), (2, 1), (2, 6), (3, 4), (4, 3), (5, 1), (5, 6), (6, 0),
      (6, 5)},
    {(0, 1), (0, 6), (2, 0), (2, 2), (2, 5), (3, 1), (3, 6), (4, 1), (4, 6), (5, 0), (5, 2),
      (5, 5)}]

end ClassicalSchur
Source
A. McKenna, "The Schur degree of block sums: L(4) = 16 and L(5) ≥ 49", Zenodo (2026), https://doi.org/10.5281/zenodo.22987189, §3 (the sequence W; Lemma 3.1; Lemma 3.2: the classes C₀, C₁, C₂) and §5, proof of Theorem 1.2 (the four sets that partition ℤ₇ × ℤ₇ ∖ {0}). Lean source: https://github.com/mysticflounder/schur-degree-block-sums/blob/v1.0.1/lean/ClassicalSchur/Values.lean#L27-L33 and https://github.com/mysticflounder/schur-degree-block-sums/blob/v1.0.1/lean/ClassicalSchur/Values.lean#L84-L94 (release v1.0.1, doi:10.5281/zenodo.22987688).

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