Invited Article Foreword

Abstract

The Invited Article section of this issue includes “The Reachability Problem for Petri Nets Is Not Elementary,” by Wojciech Czerwiński, Sławomir Lasota, Ranko Lazić, Jérôme Leroux, and Flip Mazowiecki, which won the best paper award at the 51st Annual ACM Symposium on the Theory of Computing (STOC’19). We thank the STOC’19 Program Committee for their help in selecting this invited article, and we thank editor Martin Grohe for handling this article.