IMO Shortlist 1973 problem 6


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Dodao/la: arhiva
April 2, 2012
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Establish if there exists a finite set M of points in space, not all situated in the same plane, so that for any straight line d which contains at least two points from M there exists another straight line d', parallel with d, but distinct from d, which also contains at least two points from M.
Source: Međunarodna matematička olimpijada, shortlist 1973