Category Archives: Uncategorized

שאלה לנתניהו – הסרט, התשובה שלי, וכמה תשובות של אחרים

 מדוע פרק בנימין נתניהו את הקואליציה והממשלה במקום לחזק את הממשלה ולבסס את התמיכה בה כאשר העריך שאנו עומדים בפני עימות בנושא קיומי עם הממשל האמריקאי


התשובה שלי היא פשוטה : נתניהו כשל! יש להחליף אותו 

איזה סיבה היתה לבנימין נתניהו לפרק את הממשלה והקואליציה רק לאחר שנה וחצי ואף להסתכן בהפסד

זהו חוסר בשיקול דעת שמבטא זיהוי מופרז של אינטרסים שלו עם אינטרסים של המדינה ומצביע גם על נטייה מיותרת להימור ועל קריאה מאד לא נכונה של המציאות. אלה לא תכונות שאתה רוצה לראות אצל ראש ממשלה באיזור שלנו

הנה קישור לפוסט המקורי ולדיון בו, והנה מספר תשובות שמשתתפים בפורומים אחרים הציעו

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Combinatorics and More – Greatest Hits

True Mathematics - Greatest Hits (Vinyl-1988) (2)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)
Rationality, Economics and Games

Open problems

Five Open Problems Regarding Convex Polytopes
Seven Problems Around Tverberg’s Theorem
F ≤ 4E
The AC0 Prime Number Conjecture
Coloring Simple Polytopes and Triangulations
Some old and new problems in combinatorics and geometry
Noise Stability and Threshold Circuits

Taxi and other Stories

Cosmonaut: Michal Linial
Michal Linial: No Witches in Portugal
Tel-Aviv’s “Jerusalem Beach”
Coffee, Cigarettes, and Aggression


Ziegler´s Lecture on the Associahedron  Continue reading

From Peter Cameron’s Blog: The symmetric group 3: Automorphisms

Gil Kalai:

Here is, with Peter’s kind permission, a rebloging of Peter’s post on the automorphism group of S_n. Other very nice accounts are by the Secret blogging seminar;  John Baez,; A paper by Howard, Millson, Snowden, and Vakil; and most famously the legendary Chapter 6 (!) from the book by Cameron and Van-Lint (I dont have an electronic version for it).

My TYI 25 question about it arose from Sonia Balagopalan’s lecture in our combinatorics seminar on the 16 vertex triangulation of 4-dimensional projective space. (Here is the link to her paper.)

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.

Here are the definitions. An automorphism of a group G is a permutation p of the group which preserves products, that is, (xy)p=(xp)(yp) for all x,y (where, as a card-carrying algebraist, I write the function on the right of its argument). The automorphisms of G themselves form a group, and the inner automorphisms (the conjugation maps x?g-1xg) form a normal subgroup; the factor group is the outer automorphism group of G. Abusing terminology, we say that G has outer automorphisms if the outer automorphism group is not the trivial group, that is, not all automorphisms are inner.

Now the symmetric group S

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Media items on David, Amnon, and Nathan


David Kazhdan, a very famous mathematician from my department with a super-human understanding of mathematics (and more) is recovering from a terrible bike accident. Here is an article about him from “Maariv.” (In Hebrew)



Amnon Shashua, a  computer science professor at the Hebrew University founded Mobileye fifteen years ago. Here is one of many articles about Mobileye. Mobileye helps eliminate car accidents and her sister company Orcam that Amnon also founded develops aids for the visually impaired.


Nathan Keller, now at Bar-Ilan University,  is a former Ph D student of mine working in probabilistic combinatorics and he has a parallel impressive academic career in the area of cryptology. Here is an article about Nathan from Arutz 7 (in Hebrew).   (The picture above shows Nathan with Eli Biham and Elad Barkan after their 2003 success in cracking the popular GSM cellular phone network encryption code.)


Dorit Aharonov’s on TEDx: A Feldenkrais lesson for the beginner scientist

Here is a lovely lecture starting with quantum computers, going through the Feldenkrais method, and ending with a mathematical puzzle.


Click on the picture for the video of the talk.

Here are Dorit’s four body-mind principles for learning:

1. Start within your comfort zone and make it even more conforting,

2. Not too easy not too hard, pick an interesting challenge within your reach,

3. Move away from your desired place and come back to it from different angles,

4. Play with it, connect it with other things you know, make it your own.

Course Announcement: High Dimensional Expanders

lubotzky picture

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 on Tuesdays 10-12.

Topics will include:

  • Some background on expander graphs and on simplicial complexes and homology 
  • The geometric definition of high dimensional expanders in the recent paper: Overlap properties of geometric expanders.  by J. Fox, M. Gromov, V. Lafforgue, A. Naor, and J. Pach;
  • A cohomological definition arising in Linial-Meshulam’s work about homology of random complexes;  possible definitions based on high Laplacians,
  • Ramanujan complexes; 
  • Potential applications to error correcting codes and quantum error correcting codes.

(I will add further relevant links, and a more detailed description later.)