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arxiv: 1202.3110 · v2 · pith:OMFYQCYOnew · submitted 2012-02-14 · 🧮 math.CO · cs.CG

A Pseudoline Counterexample to the Strong Dirac Conjecture

classification 🧮 math.CO cs.CG
keywords pointspseudolinesconjecturediracincidencespseudolinestrongstructure
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We demonstrate an infinite family of pseudoline arrangements, in which an arrangement of n pseudolines has no member incident to more than 4n/9 points of intersection. This shows the "Strong Dirac" conjecture to be false for pseudolines. We also raise a number of open problems relating to possible differences between the structure of incidences between points and lines versus the structure of incidences between points and pseudolines.

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