Hanssen, Calvin, Fransiskus Fran, and Yundari Yundari. “The Complexity of Pencil Graph and Line Pencil Graph”. PYTHAGORAS Jurnal Matematika dan Pendidikan Matematika 19, no. 2 (November 18, 2024): 115–125. Accessed July 9, 2025. https://journal.uny.ac.id/index.php/pythagoras/article/view/77747.