Cranston, Daniel W., and Gexin Yu. “A New Lower Bound on the Density of Vertex Identifying Codes for the Infinite Hexagonal Grid”. The Electronic Journal of Combinatorics 16, no. 1 (September 18, 2009): R113. Accessed March 16, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v16i1r113.