Category Archives: Conferences

From Oberwolfach: The Topological Tverberg Conjecture is False

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 based on two major ingredients. The first is a recent major theory by Issak Mabillard and Uli Wagner which extends fundamental theorems from classical obstruction theory for embeddability to an obstruction theory for r-fold intersection of disjoint faces in maps from simplicial complexes to Euclidean spaces. An extended abstract of this work is Eliminating Tverberg points, I. An analogue of the Whitney trick. The second is a result  by Murad Özaydin’s from his 1987 paper Equivariant maps for the symmetric group, which showed that for the non prime-power case the topological obstruction vanishes.

It was commonly believed that the topological Tverberg conjecture is correct. However, one of the motivations of Mabillard and Wagner for studying elimination of higher order intersection was that this may lead to counterexamples via Özaydin result. Isaak and Uli came close but there was a crucial assumption of large codimension in their theory, which seemed to avoid applying the new theory to this case.  It turned out that a simple combinatorial argument allows to overcome the codimension problem!

Florian’s  combinatorial argument which allows to use Özaydin’s result in Mabillard-Wagner’s theory  is a beautiful example of a powerful combinatorial method with other applications by Pavle Blagojević, Florian Frick and Günter Ziegler.


Both Uli and Florian talked about it here at Oberwolfach on Tuesday. I hope to share some more news items from Oberwolfach and from last week’s Midrasha in future posts.

Midrasha Mathematicae #18: In And Around Combinatorics



Tahl Nowik

photo (4) 17.8.14 midrasha poster 2015 poster

michal-mid mid-irit mid-david nati-mid mid-peter nica-mid   alex-mid2 midjoel mid-sam tami-mid zohar-mid tahl-mid

Update 3 (January 30): The midrasha ended today. Update 2 (January 28): additional videos are linked; Update 1 (January 23): Today we end the first week of the school. David Streurer and Peter Keevash completed their series of lectures and Alex Postnikov started his series.


Today is the third day of our winter school. In this page I will gradually give links to to various lectures and background materials. I am going to update the page through the two weeks of the Midrasha. Here is the web page of the midrasha, and here is the program. I will also present the posters for those who want me to: simply take a picture (or more than one) of the poster and send me. And also – links to additional materials, pictures, or anything else: just email me, or add a comment to this post.

Lecture series and lectures

Irit Dinur: Direct products of games and graphs

mid-irit Continue reading

A Historical Picture Taken by Nimrod Megiddo

Last week I took a bus from Tel Aviv to Jerusalem and I saw (from behind) a person that I immediately recognized. It was Nimrod Megiddo, from IBM Almaden, one of the very first  to relate game theory with complexity theory, one of the pioneers of computational geometry, and one of the leaders in optimization and linear programming, the guy who (with Ehud Kalai) was the first to  invited me to an international conference, and a fresh Laureate of the John von Neumann theory Prize.  I did not see Nimrod more than a year after our last coincidental  meeting at the Berkeley Simons Institute, I called over to him and he was happy to see me as I was happy to see him, and we found a place together at the back of the bus and caught up on things.

Nimrod showed me on the bus a picture he found in his house, taken by him at the  1974  game theory workshop in Bad Salzuflen, Germany. With Nimrod’s kind permission I present the picture here: (The copyright © belongs to Nimrod Megiddo who took the picture).


Here are some of the people left to right, (on some I already told you in other posts):

David Schmeidler (only beard visible)
Guillermo Owen
Lloyd Shapley
Sergiu Hart
Yair Tauman (only back shown)
Robert Aumann
Werner Güth (behind Aumann)
Reinhard Selten
Ehud Kalai (just to the right of Selten looking at the camera)
Gerhard Schwedihauer
Elon Kohlberg (only back shown, looking to the left)
William Lucas (in the back, looking at the wall)
Robert Weber (only hair and jacket visible)
Bezalel Peleg (looking to the right)
Joel Moulen (looking to the left)
Thomas Marschak (sunglasses and beard)
Michael Maschler
Joachim Rosenmüller (with glasses behind Maschler)
Kenjiro Nakamura

Happy new 2015!

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 Alon’s lecture in the meeting. Noga is my genious twin academic brother – we both were graduate students under the supervision of Micha A. Perles in the same years and we both went to MIT as postocs in fall 1983.  The lecture starts with briefly mentioning four results by the birthday boys related to combinatorics and geometry and continues with recent startling results by Alon, Ankur Moitra, and Benny Sudakov. One out of many contributions of Noga over the years is building a large infrastructure of constructions and examples, often very surprising,  in combinatorics, graph theory, information theory,TOC, and related areas. And the new results add to this infrastructure. The slides are very clear. Enjoy!






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

17.8.14 midrasha poster 2015 (1)


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 for local and travel expences are possible.


Media Item from “Haaretz” Today: “For the first time ever…”


Maryam Mirzakhani received the medal from South Korea’s president Park Geun-hye. 

Here is an article from today’s Israeli newspaper Haaretz.  It is based on this article by the Guardian (Thanks, Manor!).  See also this post on Laba’s accidental mathematician and John Baez’ Google+ post.

The ICM 2014 started today in Seoul. The International congress taking place once every four years is an exciting event, celebrated by thousands of mathematicians in Seoul and many others all over the world. The opening ceremonies came with the announcement of  Artur Avila, Manjul Bhargava, Martin Hairer, and Maryam Mirzakhani as 2014 Fields medalist, Subhash Khot won the Nevanlinna prize, Stanley Osher won the Gauss prize and Phillip Griffiths is the Chern medalist, and  Adrián Paenza won the Leelavati Prize. Heartly congratulations to Artur, Manjul, Martin, Maryam, Subhash, Stanley, Phillip, and Adrián! This is also the first for Brazil, Austria, Canada, and Iran! More on the Fields medalists works can be found on Terry Tao’s blog. (New) And here is a live bloging (with pictures) on ICM2014 day 1 from Gowers’s blog.   And also here from the ICM site on the work of all prize recipients. And from Quanta Magazine: (More) More on Osher, Griffiths, and Khot on terry Tao’s blog, on Khot on Scott Aaronson’s blog and on a description of the laudations on Gowers blog.