Mukkamala, Padmini, János Pach, and Dömötör Pálvölgyi. “Lower Bounds on the Obstacle Number of Graphs”. The Electronic Journal of Combinatorics 19, no. 2 (June 6, 2012): #P32. Accessed May 5, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v19i2p32.