Hoffman’s bound (or: ratio bound) on the size of a coclique (or: independent set, stable set) in a graph is one of the most important bounds in spectral graph theory. At the same time it is often misattributed. Primary reason for is that Hoffman never published it, but people want to cite something for it. […]
I started writing this blog post some months ago. Occasion was that my paper “A construction for clique-free pseudorandom graphs” (in joint work Anurag Bishnoi and Valentina Pepe) was accepted by Combinatorica with minor revisions. More precisely, one of the referees was unfavorable of publication because he got the impressions that we are simply restating […]
1. Introduction The following is mostly based on texts by Cordula Tollmien. I thank John Bamberg for his assistance, and Cordula Tollmien and Cheryl Praeger for their helpful comments on earlier drafts of this text. Emmy Noether is one the most influential mathematicians of all time and one of the shining examples of the mathematics […]