The discovery of an engraved geometrical pattern on one of the shells came as a total surprise. The zig zag pattern, that can only be seen with oblique lighting, is clearly older than the ...

Infinitely many copies of a 13-sided shape can be arranged with no overlaps or gaps in a pattern that never repeats. David Smith, Joseph Samuel Myers, Craig S. Kaplan and Chaim Goodman-Strauss (CC ...