<p>Dirac and Motzkin conjectured that any set <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2025_2913_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {X}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">X</mi> </math></EquationSource> </InlineEquation> of <i>n</i> non-collinear points in the plane has an element incident with at least <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2025_2913_Article_IEq2.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="31" /> </InlineMediaObject> <EquationSource Format="TEX">\(\lceil \frac{n}{2} \rceil \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>⌈</mo> <mfrac> <mi>n</mi> <mn>2</mn> </mfrac> <mo>⌉</mo> </mrow> </math></EquationSource> </InlineEquation> lines spanned by&#xa0;<InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2025_2913_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {X}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">X</mi> </math></EquationSource> </InlineEquation>. In this paper we prove that any set <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2025_2913_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {X}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">X</mi> </math></EquationSource> </InlineEquation> of <i>n</i> non-collinear points in the plane, distributed on three lines passing through a common point, has an element incident with at least <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2025_2913_Article_IEq2.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="31" /> </InlineMediaObject> <EquationSource Format="TEX">\(\lceil \frac{n}{2} \rceil \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>⌈</mo> <mfrac> <mi>n</mi> <mn>2</mn> </mfrac> <mo>⌉</mo> </mrow> </math></EquationSource> </InlineEquation> lines spanned by <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2025_2913_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {X}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">X</mi> </math></EquationSource> </InlineEquation>.</p>

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On Dirac and Motzkin Problem in Discrete Geometry

  • Jan Florek

摘要

Dirac and Motzkin conjectured that any set \(\mathcal {X}\) X of n non-collinear points in the plane has an element incident with at least \(\lceil \frac{n}{2} \rceil \) n 2 lines spanned by  \(\mathcal {X}\) X . In this paper we prove that any set \(\mathcal {X}\) X of n non-collinear points in the plane, distributed on three lines passing through a common point, has an element incident with at least \(\lceil \frac{n}{2} \rceil \) n 2 lines spanned by \(\mathcal {X}\) X .