Monthly Archives: August 2017

Micha Perles’ Geometric Proof of the Erdos-Sos Conjecture for Caterpillars

A geometric graph is a set of points in the plane (vertices) and a set of line segments between certain pairs of points (edges). A geometric graph is simple if the intersection of  two edges is empty or a vertex … Continue reading

Posted in Combinatorics, Geometry | Tagged , | 1 Comment

Touching Simplices and Polytopes: Perles’ argument

Joseph Zaks (1984), picture taken by Ludwig Danzer (OberWolfach photo collection)   The story I am going to tell here was told in several places, but it might be new to some readers and I will mention my own angle, … Continue reading

Posted in Combinatorics, Convex polytopes, Geometry, Open problems | Tagged , | Leave a comment

Where were we?

I was slow blogging, and catching up won’t be so easy. Of course, this brings me back to the question of what I should blog about. Ideally, I should tell you about mathematical things I heard about. The problem is … Continue reading

Posted in Combinatorics, Conferences, Movies, Updates | Tagged , | 2 Comments