Kovács, István, and Géza Tóth. “Multiple Coverings With Closed Polygons”. The Electronic Journal of Combinatorics 22, no. 1 (January 27, 2015): #P1.18. Accessed May 14, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v22i1p18.