Smoke signals rise from an unassuming storefront in Albuquerque, beckoning hungry souls to what might be New Mexico’s most addictive pulled pork sandwich at Whole Hog Café.

Two mathematicians have proved that a straightforward question—how hard is it to untie a knot?—has a complicated answer.

Costco, long known for its egalitarian warehouse aisles and one-size-fits-all membership, has upended its reputation with a ...