Given a set of points *S*, let *L*(*S*) be the set of all
points lying on any line connecting two distinct points in *S*. For
example if *S* is the disjoint union of a closed
line segment and a point not lying on the line containing the segment,
then *L*(*S*) consists of two vertical angles and their
interiors and the line containing the segment as shown in the figure below.
In this case, *L*(*L*(*S*)) is the entire plane.

This month's problem is to determine *L*(*L*(*S*)) when *S*
consists of the vertices of a regular tetrahedron.

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The solution will be posted shortly.
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