Keller, C., & Smorodinsky, S. (2019). A new lower bound on Hadwiger-Debrunner numbers in the plane. Acta Mathematica Universitatis Comenianae, 88(3), 855-860. Retrieved from http://www.iam.fmph.uniba.sk/amuc/ojs/index.php/amuc/article/view/1282