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 Jirka
 AviFest, AviStories and Amazing Cash Prizes.
 Polymath 10 post 6: The ErdosRado sunflower conjecture, and the Turan (4,3) problem: homological approaches.
 Polymath 10 Emergency Post 5: The ErdosSzemeredi Sunflower Conjecture is Now Proven.
 Mind Boggling: Following the work of Croot, Lev, and Pach, Jordan Ellenberg settled the cap set problem!
 More Math from Facebook
 The Erdős Szekeres polygon problem – Solved asymptotically by Andrew Suk.
 The Quantum Computer Puzzle @ Notices of the AMS
 Three Conferences: Joel Spencer, April 2930, Courant; Joel Hass May 2022, Berkeley, Jean Bourgain May 2124, IAS, Princeton
Top Posts & Pages
 The Erdős Szekeres polygon problem  Solved asymptotically by Andrew Suk.
 Believing that the Earth is Round When it Matters
 Jirka
 Answer: Lord Kelvin, The Age of the Earth, and the Age of the Sun
 Polymath 10 Emergency Post 5: The ErdosSzemeredi Sunflower Conjecture is Now Proven.
 A Breakthrough by Maryna Viazovska Leading to the Long Awaited Solutions for the Densest Packing Problem in Dimensions 8 and 24
 Amazing: Peter Keevash Constructed General Steiner Systems and Designs
 Polymath 10 post 6: The ErdosRado sunflower conjecture, and the Turan (4,3) problem: homological approaches.
 Greg Kuperberg: It is in NP to Tell if a Knot is Knotted! (under GRH!)
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Category Archives: Combinatorics
Amazing: Peter Keevash Constructed General Steiner Systems and Designs
Here is one of the central and oldest problems in combinatorics: Problem: Can you find a collection S of qsubsets from an nelement set X set so that every rsubset of X is included in precisely λ sets in the collection? … Continue reading
Many triangulated threespheres!
The news Eran Nevo and Stedman Wilson have constructed triangulations with n vertices of the 3dimensional sphere! This settled an old problem which stood open for several decades. Here is a link to their paper How many nvertex triangulations does the 3 … Continue reading
Posted in Combinatorics, Convex polytopes, Geometry, Open problems
Tagged Eran Nevo, Stedman Wilson
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NatiFest is Coming
The conference Poster as designed by Rotem Linial A conference celebrating Nati Linial’s 60th birthday will take place in Jerusalem December 1618. Here is the conference’s webpage. To celebrate the event, I will reblog my very early 2008 post “Nati’s … Continue reading
Posted in Combinatorics, Computer Science and Optimization, Conferences, Updates
Tagged Nati Linial
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Analysis of Boolean Functions – Week 7
Lecture 11 The Cap Set problem We presented Meshulam’s bound for the maximum number of elements in a subset A of not containing a triple x,y,x of distinct elements whose sum is 0. The theorem is analogous to Roth’s theorem … Continue reading
Posted in Combinatorics, Computer Science and Optimization, Teaching
Tagged Cap set problem, Codes, Linearity testing
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Analysis of Boolean Functions week 5 and 6
Lecture 7 First passage percolation 1) Models of percolation. We talked about percolation introduced by Broadbent and Hammersley in 1957. The basic model is a model of random subgraphs of a grid in ndimensional space. (Other graphs were considered later as … Continue reading
Posted in Combinatorics, Computer Science and Optimization, Probability, Teaching
Tagged Arrow's theorem, Percolation
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Analysis of Boolean Functions – week 4
Lecture 6 Last week we discussed two applications of the FourierWalsh plus hypercontractivity method and in this lecture we will discuss one additional application: The lecture was based on a 5pages paper by Ehud Friedgut and Jeff Kahn: On the number … Continue reading
Analysis of Boolean Functions – Week 3
Lecture 4 In the third week we moved directly to the course’s “punchline” – the use of FourierWalsh expansion of Boolean functions and the use of Hypercontractivity. Before that we started with a very nice discrete isoperimetric question on a … Continue reading
Richard Stanley: How the Proof of the Upper Bound Theorem (for spheres) was Found
The upper bound theorem asserts that among all ddimensional polytopes with n vertices, the cyclic polytope maximizes the number of facets (and kfaces for every k). It was proved by McMullen for polytopes in 1970, and by Stanley for general triangulations … Continue reading
Analysis of Boolean functions – week 2
Post on week 1; home page of the course analysis of Boolean functions Lecture II: We discussed two important examples that were introduced by BenOr and Linial: Recursive majority and tribes. Recursive majority (RM): is a Boolean function with variables … Continue reading
Posted in Combinatorics, Computer Science and Optimization, Probability, Teaching
Tagged Boolean functions, Tribes
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Around Borsuk’s Conjecture 3: How to Save Borsuk’s conjecture
Borsuk asked in 1933 if every bounded set K of diameter 1 in can be covered by d+1 sets of smaller diameter. A positive answer was referred to as the “Borsuk Conjecture,” and it was disproved by Jeff Kahn and me in 1993. … Continue reading