The Erdős-Anning theorem states that every point set in the Euclidean plane with integer distances must be either collinear or finite. More strongly, for any (non-degenerate) triangle of diameter δ, at most O(δ²) points can have integer distances from all three triangle vertices. We prove the same results for any strictly convex distance function on the plane, and analogous results for every two-dimensional complete Riemannian manifold of bounded genus and for geodesic distance on the boundary of every three-dimensional Euclidean convex set. As a consequence, we resolve a 1983 question of Richard Guy on the equilateral dimension of Riemannian manifolds. Our proofs are based on the properties of additively weighted Voronoi diagrams of these distances.
@InProceedings{eppstein:LIPIcs.SoCG.2025.46, author = {Eppstein, David}, title = {{Non-Euclidean Erd\H{o}s-Anning Theorems}}, booktitle = {41st International Symposium on Computational Geometry (SoCG 2025)}, pages = {46:1--46:15}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-370-6}, ISSN = {1868-8969}, year = {2025}, volume = {332}, editor = {Aichholzer, Oswin and Wang, Haitao}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2025.46}, URN = {urn:nbn:de:0030-drops-231983}, doi = {10.4230/LIPIcs.SoCG.2025.46}, annote = {Keywords: integer distances, additively weighted Voronoi diagrams, convex distance functions, Riemannian manifolds, geodesic distance} }
Feedback for Dagstuhl Publishing