Monthly Archives: May 2019

A sensation in the morning news – Yaroslav Shitov: Counterexamples to Hedetniemi’s conjecture.

Posted on May 10, 2019 by Gil Kalai

Two days ago Nati Linial sent me an email entitled “A sensation in the morning news”. The link was to a new arXived paper by Yaroslav Shitov: Counterexamples to Hedetniemi’s conjecture. Hedetniemi’s 1966 conjecture asserts that if and are two … Continue reading →

Posted in Combinatorics, Open problems, Updates | Tagged , | 18 Comments

Answer to TYI 37: Arithmetic Progressions in 3D Brownian Motion

Posted on May 7, 2019 by Gil Kalai

Consider a Brownian motion in three dimensional space. We asked (TYI 37) What is the largest number of points on the path described by the motion which form an arithmetic progression? (Namely, , so that all are equal.) Here is … Continue reading →

Posted in Combinatorics, Open discussion, Probability | Tagged , , | 1 Comment

The last paper of Catherine Rényi and Alfréd Rényi: Counting k-Trees

Posted on May 1, 2019 by Gil Kalai

A k-tree is a graph obtained as follows: A clique with k vertices is a k-tree. A k-tree with n+1 vertices is obtained from a k-tree with n-vertices by adding a new vertex and connecting it to all vertices of a … Continue reading →

Posted in Combinatorics, People | Tagged , , | 8 Comments