Update on “the hat”: It’s “the spectre,” a single shape that can tile the plane aperiodically but not periodically, and doesn’t require flipping

Last year we reported on “The hat”: A single shape that can tile the plane aperiodically but not periodically. A commenter pointed out that the aperiodic “hat” tiling included mirror reflections, which led to the question of whether there’s a … Continue reading → …