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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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Claim. D. Neiman, J. Mackey and M. J. H. Heule, Tighter bounds on directed Ramsey number R(7)R(7), Graphs Combin. 38 (2022), no. 5, Paper No. 156, prove 34≤R(7)≤4734\le R(7)\le47 (Section 5 of the library's source card). The upper bound says that every tournament on 4747 vertices contains a transitive subtournament on 77 vertices, so f(n)≥7f(n)\ge7 for every n≥47n\ge47, while the formula of Problem 1216 gives ⌊log⁡2n⌋+1=6\lfloor\log_2n\rfloor+1=6 for 32≤n≤6332\le n\le63; the formula fails for 47≤n≤6347\le n\le63, values that include some, 47≤n≤5347\le n\le53, below the reach of the Sánchez-Flores bounds. The lower bound is an explicit 3333-vertex tournament with no transitive 77-subtournament, so f(33)=6f(33)=6. Both bounds are computer-assisted: the upper bound is a SAT-based case analysis of the in- and out-degrees of a 4747-vertex tournament with no transitive 77-subtournament, built on the authors' classification of the tournaments on 2323 to 2525 vertices with no transitive 66-subtournament.

Depends on. Reid and Parker 1970 for R(6)≤28R(6)\le28 (their Corollary 1 at k=6k=6), which bounds every in-degree of a tournament with no transitive 77-subtournament by 2727; the paper cites R(6)=28R(6)=28 to Sánchez-Flores 1994.

Source. The page is dated by the first arXiv posting, 2 November 2020; the journal version was published online on 9 September 2022 (per Crossref). The locators of the source card are to the NSF author manuscript.

Acceptance. Refereed: Graphs and Combinatorics 38 (2022), no. 5, Paper No. 156. The site's commentary does not cite this paper, so no reviewed evidence is listed. The computations are not replayed in this corpus.