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Recent Posts
- To cheer you up in difficult times 21: Giles Gardam lecture and new result on Kaplansky’s conjectures
- Nostalgia corner: John Riordan’s referee report of my first paper
- At the Movies III: Picture a Scientist
- At the Movies II: Kobi Mizrahi’s short movie White Eye makes it to the Oscar’s short list.
- And the Oscar goes to: Meir Feder, Zvi Reznic, Guy Dorman, and Ron Yogev
- Thomas Vidick: What it is that we do
- To cheer you up in difficult times 20: Ben Green presents super-polynomial lower bounds for off-diagonal van der Waerden numbers W(3,k)
- To cheer you up in difficult times 19: Nati Linial and Adi Shraibman construct larger corner-free sets from better numbers-on-the-forehead protocols
- Possible future Polymath projects (2009, 2021)
Top Posts & Pages
- To Cheer You Up in Difficult Times 15: Yuansi Chen Achieved a Major Breakthrough on Bourgain's Slicing Problem and the Kannan, Lovász and Simonovits Conjecture
- To cheer you up in difficult times 21: Giles Gardam lecture and new result on Kaplansky's conjectures
- TYI 30: Expected number of Dice throws
- 8866128975287528³+(-8778405442862239)³+(-2736111468807040)³
- The Argument Against Quantum Computers - A Very Short Introduction
- Answer: Lord Kelvin, The Age of the Earth, and the Age of the Sun
- Amazing: Zhengfeng Ji, Anand Natarajan, Thomas Vidick, John Wright, and Henry Yuen proved that MIP* = RE and thus disproved Connes 1976 Embedding Conjecture, and provided a negative answer to Tsirelson's problem.
- Possible future Polymath projects (2009, 2021)
- Photonic Huge Quantum Advantage ???
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Monthly Archives: June 2008
The Golden Room and the Golden Mountain
Christine Björner’s words at the Stockholm Festive Combinatorics are now available to all our readers. What makes this moving and interesting, beyond the intimate context of the conference, is our (mathematician’s) struggle (and usually repeated failures) to explain to … Continue reading
Amir Ban on Deep Junior
Ladies and Gentelmen: Amir Ban (right, in the picture above) the guest blogger, was an Israeli Olympiad math champion in the early 70s, with Shay Bushinsky he wrote Deep Junior, and he is also one of the inventors of the “disc on … Continue reading
Euler’s Formula, Fibonacci, the Bayer-Billera Theorem, and Fine’s CD-index
Bill Gessley proving Euler’s formula (at UMKC) In the earlier post about Billerafest I mentioned the theorem of Bayer and Billera on flag numbers of polytopes. Let me say a little more about it. 1. Euler Euler’s theorem asserts that for … Continue reading
Posted in Combinatorics, Convex polytopes
Tagged Bayer-Billera's theorem, CD-index, Flag numbers, Jonathan Fine, Lou Billera, Marge Bayer
7 Comments
Helly’s Theorem, “Hypertrees”, and Strange Enumeration II: The Formula
In the first part of this post we discussed an appealing conjecture regaring an extension of Cayley’s counting trees formula. The number of d-dimensional “hypertrees” should somehow add up to . But it was not clear to us which complexes we want … Continue reading
Posted in Combinatorics, Convexity
Tagged Cayley theorem, Helly type theorems, Topological combinatorics
6 Comments
Optimism – two quotes
1. Here is a quote from Karl Popper’s paper “Science, Problems, Aims, Responsibilities” about Francis Bacon: “According to Bacon, nature, like God, was present in all things, from the greatest to the least. And it was the aim or the … Continue reading
Billerafest
I am unable to attend the conference taking place now at Cornell, but I send my warmest greetings to Lou from Jerusalem. The titles and abstracts of the lectures can be found here. Let me tell you about two theorems by Lou. … Continue reading
Posted in Conferences, Convex polytopes
Tagged f-vectors, flag vectors, g-conjecture, Lou Billera
1 Comment
Helly’s Theorem, “Hypertrees”, and Strange Enumeration I
1. Helly’s theorem and Cayley’s formula Helly’s theorem asserts: For a family of n convex sets in , n > d, if every d+1 sets in the family have a point in common then all members in the family have a point in common. … Continue reading
Posted in Combinatorics, Convexity
Tagged Cayley theorem, Helly Theorem, Simplicial complexes, Topological combinatorics, Trees
9 Comments
A Small Debt Regarding Turan’s Problem
Turan’s problem asks for the minimum number of triangles on n vertices so that every 4 vertices span a triangle. (Or equivalently, for the maximum number of triangles on n vertices without a “tetrahedron”, namely without having four triangles on … Continue reading