  A sphere packing of the three-dimensional Euclidean space is compact if it
has only tetrahedral holes, that is, any local maximum of the distance to the
spheres is at equal distance to exactly four spheres. This papers describes all
the compact packings with spheres of three different sizes. They are
close-compact packings of unit spheres with holes filled in four different ways
by smaller spheres.

Metric Geometry;Discrete Mathematics