## A short nonalgorithmic proof of the containers theorem for hypergraphs

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- by Anton Bernshteyn, Michelle Delcourt, Henry Towsner and Anush Tserunyan PDF
- Proc. Amer. Math. Soc.
**147**(2019), 1739-1749

## Abstract:

Recently the breakthrough method of hypergraph containers, developed independently by Balogh, Morris, and Samotij [J. Amer. Math. Soc. 28 (2015), pp. 669–709] as well as Saxton and Thomason [Invent. Math. 201 (2015), pp. 925–992], has been used to study sparse random analogs of a variety of classical problems from combinatorics and number theory. The previously known proofs of the containers theorem use the so-called*scythe algorithm*—an iterative procedure that runs through the vertices of the hypergraph. (Saxton and Thomason [Combin. Probab. Comput. 25 (2016), pp. 448–459] have also proposed an alternative, randomized construction in the case of simple hypergraphs.) Here we present the first known deterministic proof of the containers theorem that is not algorithmic, i.e., it does not involve an iterative process. Our proof is less than four pages long while being entirely self-contained and conceptually transparent. Although our proof is completely elementary, it was inspired by considering hypergraphs in the setting of nonstandard analysis, where there is a notion of dimension capturing the logarithmic rate of growth of finite sets. Before presenting the proof in full detail, we include a one page informal outline that refers to this notion of dimension and summarizes the essence of the argument.

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## Additional Information

**Anton Bernshteyn**- Affiliation: Department of Mathematics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
- MR Author ID: 1104079
- Email: bernsht2@illinois.edu
**Michelle Delcourt**- Affiliation: School of Mathematics, University of Birmingham, Birmingham B15 2TS, United Kingdom
- MR Author ID: 923919
- Email: m.delcourt@bham.ac.uk
**Henry Towsner**- Affiliation: Department of Mathematics, University of Pennsylvania, Philadelphia, Pennsylvania 19104
- MR Author ID: 745396
- Email: htowsner@math.upenn.edu
**Anush Tserunyan**- Affiliation: Department of Mathematics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
- MR Author ID: 853942
- Email: anush@illinois.edu
- Received by editor(s): January 22, 2018
- Received by editor(s) in revised form: January 24, 2018, and August 30, 2018
- Published electronically: January 9, 2019
- Additional Notes: The second author’s research was partially supported by EPSRC grant EP/P009913/1 and NSF Graduate Research Fellowship DGE 1144245.

The third author’s research was partially supported by NSF Grant DMS-1600263.

The fourth author’s research was partially supported by NSF Grant DMS-1501036. - Communicated by: Patricia L. Hersh
- © Copyright 2019 by the authors
- Journal: Proc. Amer. Math. Soc.
**147**(2019), 1739-1749 - MSC (2010): Primary 03C20, 05C35, 05C65, 05C69
- DOI: https://doi.org/10.1090/proc/14368
- MathSciNet review: 3910438