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No. LXXIX

Here is a very simple and symmetrical arrangement, by which on a board of 36 squares twelve counters are so placed that there are two, and two only, on each line, column, and diagonal.

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There are other arrangements which fulfil the conditions.

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No. LXXXI

In this nest of triangles of five tiers there are 1196 separate triangles, or nearly double the number (653) of a similar nest of four tiers.