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 Reflections: On the Occasion of Ron Adin’s and Yuval Roichman’s Birthdays, and FPSAC 2021
 ICM 2018 Rio (5) Assaf Naor, Geordie Williamson and Christian Lubich
 Test your intuition 47: AGCGTCTGCGTCTGCGACGATC? what comes next in the sequence?
 Cheerful news in difficult times: Richard Stanley wins the Steele Prize for lifetime achievement!
 Combinatorial Theory is Born
 To cheer you up in difficult times 34: Ringel Circle Problem solved by James Davies, Chaya Keller, Linda Kleist, Shakhar Smorodinsky, and Bartosz Walczak
 Good Codes papers are on the arXiv
 To cheer you up in difficult times 33: Deep learning leads to progress in knot theory and on the conjecture that KazhdanLusztig polynomials are combinatorial.
 The Logarithmic Minkowski Problem
Top Posts & Pages
 The Argument Against Quantum Computers  A Very Short Introduction
 Answer: Lord Kelvin, The Age of the Earth, and the Age of the Sun
 Reflections: On the Occasion of Ron Adin's and Yuval Roichman's Birthdays, and FPSAC 2021
 TYI 30: Expected number of Dice throws
 The Intermediate Value Theorem Applied to Football
 Gil's Collegial Quantum Supremacy Skepticism FAQ
 Zur Luria on the nQueens Problem
 Amazing: Karim Adiprasito proved the gconjecture for spheres!
 ICM 2018 Rio (5) Assaf Naor, Geordie Williamson and Christian Lubich
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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 BayerBillera Theorem, and Fine’s CDindex
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 BayerBillera's theorem, CDindex, Flag numbers, Jonathan Fine, Lou Billera, Marge Bayer
8 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 ddimensional “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 fvectors, flag vectors, gconjecture, 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
10 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