No less a mind than Bertrand Russell, of Principia Mathematica fame, was responsible for this paradox, which opened a hole in math. It’s those barbers. The Barber Paradox shows that barbers are not to ...

We recently wrote about how infinitely large sets are not all the same size as each other, but we were a bit vague about what we meant by a set. The people who invented set theory also started out ...