MathDB
TOT 072 1984 Autumn J3 M points in plane, replace line segments

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August 24, 2019
segmentscombinatorial geometrypointsgeometry

Problem Statement

On a plane there is a finite set of MM points, no three of which are collinear . Some points are joined to others by line segments, with each point connected to no more than one line segment . If we have a pair of intersecting line segments ABAB and CDCD we decide to replace them with ACAC and BDBD, which are opposite sides of quadrilateral ABCDABCD. In the resulting system of segments we decide to perform a similar substitution, if possible, and so on . Is it possible that such substitutions can be carried out indefinitely?
(V.E. Kolosov)