Mathematicians have long tried to solve a problem: finding a single shape that could tile a plane in a nonrepeating pattern. That's called an “einstein,” which comes from the German “ein stein,” or “one stone” — more loosely, “one tile” or “one shape." A shape hobbyist says he has discovered not one, but two einsteins. https://nyti.ms/3LZSPqm | The New York Times