IMO 1992 LL SAF65

If A, B, C, and D are four distinct points in space, prove that

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IMO 1992 LL SAF65

Origin: SAF

Problem

If A, B, C, and D are four distinct points in space, prove that there is a plane P on which the orthogonal projections of A, B, C, and D form a parallelogram (possibly degenerate).