Geisberger, Robert, and Dennis Schieferdecker. “Heuristic Contraction Hierarchies With Approximation Guarantee”. Proceedings of the International Symposium on Combinatorial Search 1, no. 1 (August 25, 2010): 31–38. Accessed May 26, 2026. https://ojs.aaai.org/index.php/SOCS/article/view/18161.