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 Preview: The solution by Keller and Lifshitz to several open problems in extremal combinatorics
 Basic Notions Seminar is Back! Helly Type Theorems and the Cascade Conjecture
 My Very First Book “Gina Says”, Now Published by “World Scientific”
 Itai Benjamini: Coarse Uniformization and Percolation & A Paper by Itai and me in Honor of Lucio Russo
 AfterDinner Speech for Alex Lubotzky
 Boaz Barak: The different forms of quantum computing skepticism
 Bálint Virág: Random matrices for Russ
 Test Your Intuition 33: The Great Free Will Poll
 Mustread book by Avi Wigderson
Top Posts & Pages
 Preview: The solution by Keller and Lifshitz to several open problems in extremal combinatorics
 Elchanan Mossel's Amazing Dice Paradox (your answers to TYI 30)
 Answer: Lord Kelvin, The Age of the Earth, and the Age of the Sun
 TYI 30: Expected number of Dice throws
 Basic Notions Seminar is Back! Helly Type Theorems and the Cascade Conjecture
 The KadisonSinger Conjecture has beed Proved by Adam Marcus, Dan Spielman, and Nikhil Srivastava
 A Breakthrough by Maryna Viazovska Leading to the Long Awaited Solutions for the Densest Packing Problem in Dimensions 8 and 24
 Extremal Combinatorics I: Extremal Problems on Set Systems
 Stan Wagon, TYI 23: Ladies and Gentlemen: The Answer
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Category Archives: Algebra and Number Theory
AlexFest: 60 Faces of Groups
Ladies and gentlemen, A midrasha (school) in honor of Alex Lubotzky’s 60th birthday will take place from November 6 – November 11, 2016 at the Israel Institute for Advanced Studies, the Hebrew University of Jerusalem. Don’t miss the event! And … Continue reading
Posted in Algebra and Number Theory, Combinatorics, Conferences, Updates
Tagged Alex Lubotzky
4 Comments
The Simplex, the Cyclic polytope, the Positroidron, the Amplituhedron, and Beyond
A quick schematic roadmap to these new geometric objects. The positroidron can be seen as a cellular structure on the nonnegative Grassmanian – the part of the real Grassmanian G(m,n) which corresponds to m by n matrices with all m by … Continue reading
From Peter Cameron’s Blog: The symmetric group 3: Automorphisms
Originally posted on Peter Cameron's Blog:
No account of the symmetric group can be complete without mentioning the remarkable fact that the symmetric group of degree n (finite or infinite) has an outer automorphism if and only if n=6.…
Posted in Algebra and Number Theory
2 Comments
TYI 25: The Automorphism Group of the Symmetric Group
True or False: The group of automorphisms of the symmetric group , n ≥ 3 is itself.
Posted in Algebra and Number Theory, Test your intuition
Tagged Test your intuition, the symmetric group
7 Comments
Test your intuition 24: Which of the following three groups is trivial
Martin Bridson We have three finitely presented groups A is generated by two generators a and b and one relation B is generated by three generators a, b, c and three relations , . C is generated by four generators a, b, c, d … Continue reading
Posted in Algebra and Number Theory, Test your intuition
Tagged Martin Bridson, Test your intuition
10 Comments
New Ramanujan Graphs!
Margulis’ paper Ramanujan graphs were constructed independently by Margulis and by Lubotzky, Philips and Sarnak (who also coined the name). The picture above shows Margulis’ paper where the graphs are defined and their girth is studied. (I will come back to the question … Continue reading
Posted in Algebra and Number Theory, Combinatorics, Open problems
Tagged Ramanujan graphs
10 Comments
Andrei
Andrei Zelevinsky passed away a week ago on April 10, 2013, shortly after turning sixty. Andrei was a great mathematician and a great person. I first met him in a combinatorics conference in Stockholm 1989. This was the first major … Continue reading
Primality and Factoring in Number Fields
Both PRIMALITY – deciding if an integer n is a prime and FACTORING – representing an integer as a product of primes, are algorithmic questions of great interest. I am curious to know what is known about these questions over … Continue reading
Course Announcement: High Dimensional Expanders
Alex Lubotzky and I are running together a year long course at HU on High Dimensional Expanders. High dimensional expanders are simplical (and more general) cell complexes which generalize expander graphs. The course will take place in Room 110 of the mathematics building … Continue reading
Posted in Algebra and Number Theory, Combinatorics, Geometry, Teaching
Tagged Alex Lubotzky
2 Comments
Test Your Intuition (16): Euclid’s Number Theory Theorems
Euclid’s Euclid’s book IX on number theory contains 36 propositions. The 36th proposition is: Proposition 36.If as many numbers as we please beginning from a unit are set out continuously in double proportion until the sum of all becomes prime, … Continue reading
Posted in Algebra and Number Theory, Test your intuition
Tagged Euclid, Greek mathematics
16 Comments