For those who have wrestled a bulky couch around a tight corner and lamented, “Will this ever get through?” mathematicians have heard your pleas. Geometry’s “moving sofa problem” asks for the largest ...

One idle evening last October, Mehtaab Sawhney took up an old pastime. He began perusing the website erdosproblems.com, an updated record of the 1,179 conjectures left behind by the eccentric and ...