Russell's paradox

paradox in set theory concerning the set of all sets not containing themselves

Russell's Paradox is the theory that states: If you have a list of lists that do not list themselves, then that list must list itself, because it doesn't contain itself. However, if it lists itself, it then contains itself, meaning it cannot list itself. This makes logical usages of lists of lists that don't contain themselves somewhat difficult. It was developed by Bertrand Russell.