Research Institute · Programme

Exact answers in open problems

Exact values and certified bounds on open cells in other fields: the minimal Kochen-Specker set in dimension six, Ramsey and Zarankiewicz numbers, median networks, constant-weight codes, circulant weighing matrices and universal tournaments.

Published 2026-09-06 · updated 2026-09-06

26results
3machine-checked
6negative results
6open cells

The programme

Where things stand

What this programme is about

Many branches of mathematics leave narrow gaps between upper and lower bounds on finite discrete structures. This programme resolves those finite gaps by determining exact integer values for concrete combinatorial objects. It computes the smallest circuit computing an algebraic operator, the fewest vectors admitting a quantum contextuality proof, or the densest graph avoiding forbidden subgraphs.

A resolved number provides a physical floor for applied engineering. Knowing the exact gate count of a Boolean operator prevents hardware designers from hunting for smaller implementations. Knowing the minimum comparator count for median networks guarantees optimal hardware sorting pipelines. These exact bounds also reveal where automated reasoning engines fail, pinpointing the precise structures where Boolean satisfiability solvers hit combinatorial explosions.

What has been settled

For quantum measurement sets, MF-184 eliminated 18-vector systems in C^6, improving the universal lower bound m_d ≥ 18 of Xu-Chen-Gühne (2020) and narrowing m_6 to [19, 21] alongside Lisoněk et al. (2014). MF-195 excluded 19 vectors, pushing m_6 ≥ 20; this proof repaired a constraint set to rule out a spurious (2,1,1) triple by enforcing e_3 = 0 for b' ≤ 1. MF-199 excluded 20 vectors, proving m_6 = 21 exactly, conditional on the Xu-Chen-Gühne lemma. MF-185 proved external rays share non-adjacent basis rays in orthogonality graphs.

In Boolean circuit synthesis, MF-181 proved the resolved-carry family K_m requires exact multiplicative complexity MC(K_m) = 2m + 1. MF-190 fixed the 5-input MOD3,1 B2 circuit size at 9 gates using an explicit circuit and a DRAT refutation of 8 gates; Knuth (TAOCP 7.1.2) solved n ≤ 5 by SAT with no published certificates. MF-189 certified minimal single-output median networks at 13 comparators on 7 channels and 10 comparators for the 6-channel lower median, where Dobbelaere listed 13 with no proof.

In tournament and graph combinatorics, MF-197 verified t(7) > 12 across fourteen amalgam cubes with DRAT certificates, matching Zhang-Szeider (2023). MF-198 proved every 7-universal tournament on 13 vertices has automorphism group order 1 or 3. MF-192 verified structural obstructions against 11-hosts for nine 7-tournaments, noting that t(7) > 11 is counting-trivial. MF-191 certified code size A(11,4,5) = 66 via SAT, checking a value from Brouwer's table and Östergård (2010). MF-186 showed 133-weight 16×17 Zarankiewicz matrices have maximum row degree at most 10, addressing the z(16,17;3) in {132, 133} gap from August 2026. MF-193 produced multiplier-free contraction censuses for CW(112,36), generalizing Arasu-Gordon-Zhang (2021). MF-188 proved (J4,J7;26)-graphs with minimum degree at least 9 uniquely match the vertex-deleted Schläfli complement, extending MR91.

What is still open

Solvers hit scaling barriers across several frontier cells. For tournament universality, ML-090 leaves 13 ≤ t(7) ≤ 15 undecided because CEGAR search times out at order 13. In extremal matrices, ML-091 leaves z(16,17;3) ∈ {132, 133} open; DRAT refutes row degrees 11 through 17, while eight sub-cubes stall at degrees 9 and 10. For sorting networks, ML-092 leaves median sizes open for n ≥ 8 after SAT timeouts; Smith's 1996 claim for n = 9 failed reproduction.

Circuit bounds stall under exponential costs: ML-094 leaves 6-input MOD3,0 open, where Knuth conjectures 12 gates and an 11-gate refutation timed out. In proof complexity, ML-095 leaves h_11 ≥ 28 undetermined above Peitl-Szeider's h_10 = 26, correcting the catalogue to 626,973 candidates. For codes, ML-096 leaves A(13,4,5) ∈ [123, 129] open. In algebra, ML-093 shows CW(112,36) resists DRAT and RoundingSat cutting planes due to a proof-system mismatch.

How to read the evidence

Receipted results and machine certificates dominate this programme, supported by exhaustive checks and written proofs. Machine certificates, including DRAT unsatisfiability proofs and Lean formalizations, warrant the highest trust because independent checkers verify every step without relying on solver heuristics or human referee oversight. Receipted search records guarantee reproducible computational logs. When an entry lists an empirical wall or solver timeout, it marks the technical limit of existing automated reasoning algorithms on that specific structure.

Showcase

The strongest results here

MF-184CERTIFIED PROOF

Non-existence of 18-vector Kochen-Specker sets in dimension 6

No KS set in C^6 has 18 vectors, hence m_6 >= 19 and m_6 in [19, 21]

No Kochen-Specker vector set in dimension 6 can have 18 vectors, establishing that the minimum size in dimension 6 is at least 19, conditional on one cited computational lemma.

Prior art: This result improves the universal lower bound m_d >= 18 from Xu-Chen-Guehne (2020) in dimension 6. Together with Lisonek et al. Sources: Xu, Chen, Guehne 2020 (PRL 124, 230401) · Lisonek, Badziag, Portillo, Cabello 2014 (PRA 89, 042101)

lower boundExact answers in open problemsfull paper

Published 2026-09-06

MF-189RECEIPTED

Exact sizes of small single-output median networks

n=7 median network exact size is 13 (UNSAT at 12 DRAT-verified); 6-channel lower-median exact size is 10 (UNSAT at 9 DRAT-verified).

Single-output median comparator networks have exact minimal sizes of 13 comparators on 7 channels and 10 comparators for 6-channel lower median, with lower bounds certified by DRAT proofs.

Prior art: Dobbelaere’s table lists 13 for n = 7 (unproven) and marks n = 9 as optimal (Smith 1996); Knuth TAOCP 5.3.4 remains unverified. Furthermore, a replay check confirmed Dobbelaere’s 22-comparator n = 10 network is a two-output design, correcting the single-output bound for n = 10 to 23 comparators rather than 22. Sources: Dobbelaere, median networks table

exact determinationExact answers in open problemsfull paper

Published 2026-09-06

MF-190RECEIPTED

Exact B2 circuit size and machine-checkable certificate for 5-input MOD3,1

size_B2(MOD3,1 on 5 inputs) = 9

The exact circuit size of the 5-input MOD3,1 function over the full 2-input binary basis is 9 gates, confirmed by an explicit 9-gate circuit and a machine-verified DRAT unsatisfiability certificate ruling out 8 gates.

Prior art: Knuth (TAOCP 7.1.2, exercise 480) determined the values for n ≤ 5 using SAT solving without publishing certificates. Sources: Knuth, TAOCP vol. 4A, section 7.1.2 · Kulikov, Pechenev, Slezkin 2022 (MFCS) · Kojevnikov, Kulikov, Yaroslavtsev 2009

exact determinationExact answers in open problemsfull paper

Published 2026-09-06

MF-195RECEIPTED

Nonexistence of 19-vector Kochen-Specker sets in C^6 and the lower bound m_6 ≥ 20

No KS set in C^6 has 19 vectors, hence m_6 >= 20 and m_6 ∈ {20, 21} (conditional on cited lemma as in MF-184)

There is no 19-vector Kochen-Specker set in six dimensions, proving that the minimum size m_6 is at least 20 and narrowing the true minimum to either 20 or 21, conditional on the same cited lemma as MF-184.

Prior art: Searches across existing literature found no prior work excluding 19 in d = 6, though the novelty of this result remains unverified. Sources: Xu, Chen, Guehne 2020 · Lisonek, Badziag, Portillo, Cabello 2014

lower boundExact answers in open problemsfull paper

Published 2026-09-06

MF-199RECEIPTED

Nonexistence of 20-vector Kochen-Specker sets in C^6 and minimality of m_6 = 21

No Kochen-Specker set in C^6 has 20 vectors; hence m_6 = 21 exactly, conditional on the Xu-Chen-Gühne lemma.

No Kochen-Specker set in six dimensions can have 20 vectors, proving that the minimum size in dimension six is exactly 21 vectors conditional on the Xu-Chen-Gühne lemma.

Prior art: While prior work established 18 <= m_d for all d (XCG 2020) and m_6 <= 21 (LBPC 2014, "simplest KS set admitting a symmetric parity proof"), m_6 remained in [18, 21]. Entries MF-184, MF-195, and this work close m_6 to 21, proving d = 6 is the first dimension where the bound 18 is not attained. Sources: Xu, Chen, Guehne 2020 (PRL 124, 230401) · Lisonek, Badziag, Portillo, Cabello 2014 (PRA 89, 042101)

exact determinationExact answers in open problemsfull paper

Published 2026-09-06

Every entry

The rest of the programme

Every confirmed result in this programme. Each links to its full paper.

Snapshot 2026-09-06. Generated from the division's registers and curation records; never hand-edited.