Monthly Archives: February 2015

Combinatorics and More – Greatest Hits

Posted on February 27, 2015 by Gil Kalai

Combinatorics and More’s Greatest Hits First Month Combinatorics, Mathematics, Academics, Polemics, … Helly’s Theorem, “Hypertrees”, and Strange Enumeration I (There were 3 follow up posts:) Extremal Combinatorics I: Extremal Problems on Set Systems (There were 4 follow up posts II ; III; IV; VI) Drachmas Rationality, Economics and … Continue reading →

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Ilan and me

Posted on February 23, 2015 by Gil Kalai

  With Ilan, my four month old grandson  

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The Simplex, the Cyclic polytope, the Positroidron, the Amplituhedron, and Beyond

Posted on February 16, 2015 by Gil Kalai

A quick schematic road-map 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 →

Posted in Algebra, Combinatorics, Convex polytopes, Physics | Tagged , , , , , , | 19 Comments

From Oberwolfach: The Topological Tverberg Conjecture is False

Posted on February 6, 2015 by Gil Kalai

The topological Tverberg conjecture (discussed in this post), a holy grail of topological combinatorics, was refuted! The three-page paper “Counterexamples to the topological Tverberg conjecture” by Florian Frick gives a brilliant proof that the conjecture is false. The proof is … Continue reading →

Posted in Combinatorics, Conferences, Convexity, Updates | Tagged , , , | 3 Comments