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A complete solution to the biased Alon-Krivelevich-Spencer-Szabó criterion problem for the discrepancy game Scaffolds for Higher Tropical Grassmannians: Foundations Krahn-Szegő type inequalities for graphs $\boldsymbol{2}$-Neighbor Bootstrap Percolation on Odd Graphs Modular inequalities and Alexander polynomials of pencil type conic-line arrangements Counterexamples regarding elementary symmetric partitions Bounds on Multiple $b$-Burst Deletion-Correcting Codes The mex statistic on combinatorial structures Proper Additive Edge Colorings of Regular Graphs Off-diagonal Ramsey numbers Semi-inducibility of 4-vertex graphs Bounds on the game isolation number and exact values for paths and cycles Minors of non-hamiltonian polyhedra and the Herschel family Triangle-free subsets of the $r$-distance graph of the hypercube Notes on sum-free sets in abelian groups When are Hopf algebras determined by integer sequences? 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problem A framework for large-scale distributed AI search across disconnected heterogeneous infrastructures Automorphism Groups of Graphical Models and Lifted Variational Inference Markov Chains on Orbits of Permutation Groups An Efficient Hybrid Ant Colony System for the Generalized Traveling Salesman Problem Strong Backdoors to Bounded Treewidth SAT Strong Backdoors to Nested Satisfiability e-Valuate: A Two-player Game on Arithmetic Expressions -- An Update Combinatorial frameworks for cluster algebras Backdoors to Satisfaction Backdoors to Acyclic SAT Confidence-based Reasoning in Stochastic Constraint Programming A Quantitative Version of the Gibbard-Satterthwaite Theorem for Three Alternatives Palette-colouring: a belief-propagation approach Restructuring in Combinatorial Optimization Speeding up SAT solver by exploring CNF symmetries : Revisited Input Parameters Optimization in Swarm DS-CDMA Multiuser Detectors Counting in Graph Covers: A Combinatorial Characterization of the 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Ptolemy's equation and kin
Katie Waddle · 2025-07-15 · via math.CO updates on arXiv.org

Three-term relations of the form AB+CD=EF arise in multiple mathematical contexts, including the Ptolemy equation for a cyclic quadrilateral, Casey's theorem on bitangents, Penner's relation for lambda lengths, and Plücker's identity for the maximal minors of a 2x4-matrix. In this note, we explain how these different occurrences of the 3-term relation can be directly obtained from each other.