Author Archives: Gil Kalai

@HUJI

Ilya Rips and me during Ilyafest last week (picture Itai Benjamini) Ilya Rips Birthday Conference Last week we had here a celebration for Ilya Rips’ birthday. Ilya is an extraordinary mathematician with immense influence on algebra and topology. There were … Continue reading

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When Do a Few Colors Suffice?

When can we properly color the vertices of a graph with a few colors? This is a notoriously difficult problem. Things get a little better if we consider simultaneously a graph together with all its induced subgraphs. Recall that an … Continue reading

Posted in Combinatorics | Tagged | 1 Comment

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.…

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Coloring Simple Polytopes and Triangulations

Coloring Edge-coloring of simple polytopes One of the equivalent formulation of the four-color theorem asserts that: Theorem (4CT) : Every cubic bridgeless planar graph is 3-edge colorable So we can color the edges by three colors such that every two … Continue reading

Posted in Combinatorics, Open problems | Tagged , | 10 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 , | 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 , | 10 Comments

School Starts at HUJI

We are now starting the third week of the academic year at HUJI. As usual, things are very hectic, a lot of activities in the mathematics department, in our sister CS department, around in the campus, and in our combinatorics … Continue reading

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A lecture by Noga

Noga with Uri Feige among various other heroes A few weeks ago I devoted a post to the 240-summit conference for Péter Frankl, Zoltán Füredi, Ervin Győri and János Pach, and today I will bring you the slides of Noga … Continue reading

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Ehud Friedgut: Blissful ignorance and the Kahneman-Tversky paradox

Tversky, Kahneman, and Gili Bar-Hillel (WikiPedia). Taken by Maya Bar-Hillel at Stanford, summer 1979.   The following post was kindly contributed by Ehud Friedgut. During the past week I’ve been reading, and greatly enjoying Daniel Kahneman’s brilliant book “Thinking fast … Continue reading

Posted in Guest blogger, Rationality | Tagged , , | 11 Comments

In And Around Combinatorics: The 18th Midrasha Mathematicae. Jerusalem, JANUARY 18-31

  The 18th yearly school in mathematics is devoted this year to combinatorics. It will feature lecture series by Irit Dinur, Joel Hass, Peter Keevash, Alexandru Nica, Alexander Postnikov, Wojciech Samotij, and David Streurer and additional activities. As usual grants … Continue reading

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