Fink, Martin, Sergey Pupyrev, and Alexander Wolff. “Ordering Metro Lines by Block Crossings”. Journal of Graph Algorithms and Applications 19, no. 1 (January 1, 2015): 111–153. Accessed December 6, 2025. https://jgaa-v5.cs.brown.edu/index.php/jgaa/article/view/paper351.