Data Quotes - Page 36
George Pólya (1945). “How to Solve it: A New Aspect of Mathematical Method”
George Pólya (1957). “How to solve it: a new aspect of mathematical method”
George Henry Lewes (1874). “Problems of Life and Mind: The method of science and its application to metaphysics. The rules of philosophising. Psychological principles. The limitations of knowledge”, p.17
"The City in Numbers: an Equation That Explains Urban Life". wired.co.uk, March 29, 2011.