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Search Results for: erdos
Extremal Combinatorics on Permutations
We talked about extremal problems for set systems: collections of subsets of an element sets, – Sperner’s theorem, the ErdosKoRado theorem, and quite a few more. (See here, here and here.) What happens when we consider collections of permutations rather … Continue reading
Posted in Combinatorics
Tagged ErdosKoRado theorem, Extremal combinatorics, Permutations
9 Comments
Polymath1: Success!
“polymath” based on internet image search And here is a link to the current draft of the paper. Update: March 26, the name of the post originally entitled “Polymath1: Probable Success!” was now updated to “Polymath1: Success!” It is now becoming … Continue reading
Posted in Blogging, Combinatorics, What is Mathematics
Tagged Density HalesJewett theorem, polymath1
10 Comments
FranklRodl’s Theorem and Variations on the Cap Set Problem: A Recent Research Project with Roy Meshulam (A)
Voita Rodl I would like to tell you about a research project in progress with Roy Meshulam. (We started it in the summer, but then moved to other things; so far there are interesting insights, and perhaps problems, but not substantial … Continue reading
Posted in Combinatorics, Open problems
Tagged Cap sets, Extremal combinatorics, Intersection theorems, polymath1
6 Comments
Mathematics, Science, and Blogs
Michael Nielsen wrote a lovely essay entitled “Doing science online” about mathematics, science, and blogs. Michael’s primary example is a post over Terry Tao’s blog about the NavierStokes equation and he suggests blogs as a way of scaling up scientific conversation. Michael is writing … Continue reading
Posted in Blogging, What is Mathematics
Tagged Blogs, Michael Nielsen, Open science, polymath1, Tim Gowers
5 Comments
Lior, Aryeh, and Michael
Three dear friends, colleagues, and teachers Lior Tzafriri, Aryeh Dvoretzky and Michael Maschler passed away last year. I want to tell you a little about their mathematics. Lior Tzafriri ( 19362008 ) Lior Tzafriri worked in functional analysis.
Extremal Combinatorics IV: Shifting
Compression We describe now a nice proof technique called “shifting” or “compression” and mention a few more problems. The SauerShelah Lemma: Let . Recall that a family shatters a set if for every there is such that … Continue reading
Extremal Combinatorics III: Some Basic Theorems
. Shattering Let us return to extremal problems for families of sets and describe several basic theorems and basic open problems. In the next part we will discuss a nice proof technique called “shifting” or “compression.” The SauerShelah (Perles VapnikChervonenkis) Lemma: (Here we write .) … Continue reading
Pushing Behrend Around
Erdos and Turan asked in 1936: What is the largest subset of {1,2,…,n} without a 3term arithmetic progression? In 1946 Behrend found an example with Now, sixty years later, Michael Elkin pushed the the factor from the denominator to the enumerator, … Continue reading
Posted in Combinatorics, Updates
Tagged Arithmetic progressions, Roth's theorem, Szemeredi's theorem
10 Comments
Extremal Combinatorics I: Extremal Problems on Set Systems
The “basic notion seminar” is an initiative of David Kazhdan who joined HU math department around 2000. People give series of lectures about basic mathematics (or not so basic at times). Usually, speakers do not talk about their own research and not even … Continue reading