WHAT is a boojum? Is it: a particularly dangerous variety of snark; a bizarre cactus-like tree endemic to Baja California in Mexico; or a geometrical pattern sometimes seen on the surface of ...

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 ...