<< A famous geometrical theorem called the Banach-Tarski paradox says that if you have a ball in 3-D space and split it into a few specific pieces, there is a way to reassemble the parts so that you create two balls. (..) When the two new balls are created, they will both be the same size as the first ball. >> Thomas Britz.
Sherry Landow. The mystique of mathematics: 5 beautiful math phenomena. University of New South Wales. May 20, 2020.
Banach–Tarski paradox
