Density of Binary Compact Disc Packings
A disc packing in the plane is compact if its contact graph is a triangulation. There are 9 values of r such that a compact packing by discs of radii 1 and r exists. We prove, for each of these 9 values, that the maximal density over all the packings by discs of radii 1 and r is reached for a compact packing (we give it as well as its density).
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