Cantor Diagonal Method
A clever technique used by Georg Cantor 
to show that the Integers andReals cannot be put into a One-to-One correspondence (i.e., the Uncountably Infinite Set ofReal Numbers is ``larger'' than the Countably Infinite Set of Integers).It proceeds by first considering a countably infinite list of elements from a set 
, each of which is an infinite set(in the case of the Reals, the decimal expansion of each Real). A new member
of is then created by arranging its 
th term to differ from the th term of the th member of . Thisshows that is not Countable, since any attempt to put it in one-to-one correspondence with theintegers will fail to include some elements of .
References
Courant, R. and Robbins, H. What is Mathematics?: An Elementary Approach to Ideas and Methods, 2nd ed. Oxford, England: Oxford University Press, pp. 81-83, 1996.
Penrose, R. The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics. Oxford, England: Oxford University Press, pp. 84-85, 1989.
- Quasirhombicosidodecahedron
- Quasirhombicuboctahedron
- Quasisimple Group
- Quasithin Theorem
- Quasitruncated Cuboctahedron
- Quasitruncated Dodecadocahedron
- Quasitruncated Dodecahedron
- Quasitruncated Great Stellated Dodecahedron
- Quasitruncated Hexahedron
- Quasitruncated Small Stellated Dodecahedron
- Quasi-Unipotent Group
- Quasi-Unipotent Problem
- Quaternary
- Quaternary Tree
- Quaternion
- Quattuordecillion
- Queens Problem
- Queue
- Queuing Theory
- Quicksort
- Quillen-Lichtenbaum Conjecture
- Quincunx
- Quindecillion
- Quintet
- Quintic Equation