On Lines and Joints.

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Bibliographic Details
Title: On Lines and Joints.
Authors: Kaplan, Haim1 haimk@post.tau.ac.il, Sharir, Micha michas@post.tau.ac.il, Shustin, Eugenii2 shustin@post.tau.ac.il
Source: Discrete & Computational Geometry. Dec2010, Vol. 44 Issue 4, p838-843. 6p.
Subjects: Line geometry, Algebraic curves, Mathematical proofs, Number theory, Boundary value problems, Dimensional analysis, Mathematical analysis
Abstract: Let L be a set of n lines in ℝ, for d≥3. A joint of L is a point incident to at least d lines of L, not all in a common hyperplane. Using a very simple algebraic proof technique, we show that the maximum possible number of joints of L is Θ( n). For d=3, this is a considerable simplification of the original algebraic proof of Guth and Katz (Algebraic methods in discrete analogs of the Kakeya problem, 4 December , ), and of the follow-up simpler proof of Elekes et al. (On lines, joints, and incidences in three dimensions. Manuscript, 11 May , ). Some extensions, e.g., to the case of joints of algebraic curves, are also presented. [ABSTRACT FROM AUTHOR]
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Description
Abstract:Let L be a set of n lines in ℝ, for d≥3. A joint of L is a point incident to at least d lines of L, not all in a common hyperplane. Using a very simple algebraic proof technique, we show that the maximum possible number of joints of L is Θ( n). For d=3, this is a considerable simplification of the original algebraic proof of Guth and Katz (Algebraic methods in discrete analogs of the Kakeya problem, 4 December , ), and of the follow-up simpler proof of Elekes et al. (On lines, joints, and incidences in three dimensions. Manuscript, 11 May , ). Some extensions, e.g., to the case of joints of algebraic curves, are also presented. [ABSTRACT FROM AUTHOR]
ISSN:01795376
DOI:10.1007/s00454-010-9246-3