Mathematical mystery solved by elusive 'Einstein'.

After a decade of attempts, a self-described shape hobbyist from England, David Smith, has discovered an "einstein," an aperiodic monotile that tiles a plane in a nonrepeating pattern. Smith's discovery, called "the hat," was confirmed in a new paper by Smith and three co-authors with mathematical and computational expertise. The paper provides two proofs, one of which offers a new tool for proving aperiodicity. The hat is a polykite made of eight kites and is part of an entire family of related einsteins, including a second one discovered by Smith called "the turtle."