Joint reviews of four articles

The Janos Bolyai Society has published 25 collections of articles from math conferences and I am sure they will publish more. Most are in combinatorics. We review four of them and then in the opinion section we address not only the value of these books but the value of collections like them. The first of the four, Horizons of Combinatorics is a combinatorics conference without a more detailed theme. The second and third, Building Bridges and Fete of Combinatorics and Computer Science were Volumes 1 and 2 of a conference to honor Lázló Lovasz. The papers in them were mostly combinatorics though some have a computer science flavor or application. The fourth one, Erdős Centennial is largely articles from people who spoke at the Erdős Centennial which was July 1-5 in 2013 (I was there!). Since Paul Erdős did mathematics across a wide swath or mathematics (not just combinatorics for which he is best known) the articles are in many fields. I will comment on a subset of articles from these collections. The subset is not random. It reflects my tastes and my conjecture of my readers tastes.