For 10 points, name this nineteenth century German mathematician who founded set theory.
This mathematician demonstrated that selecting a number from every diagonal decimal place on a list of the rational numbers and altering it by one digit produces a real number, proving that the rational numbers are not on a one-to-one correspondence with the real numbers. He selected the symbol aleph-null to represent the cardinality of the integers, and proved that infinite sets could be different sizes. For 10 points, name this nineteenth century German mathematician who founded set theory.
This mathematician demonstrated that selecting a number from every diagonal decimal place on a list of the rational numbers and altering it by one digit produces a real number, proving that the rational numbers are not on a one-to-one correspondence with the real numbers.
Georg {Cantor}