"Bernhard Riemann (1826–1866) was known as “the mathematician from Göttingen.” (Of course so were Gauss and Hilbert.) He provided one answer to the question, Where do functions live?, in a time in which the more general question was, Where are people to live and grow and thrive? Here, think of the First Industrial Revolution of water and steam power, the factory, and the rise of urbanization; the novels of Charles Dickens or Émile Zola; the reconstruction of Paris under Napoleon III and Haussmann; and the soon-to-come Second Industrial Revolution of electricity, chemistry, and the further transformation of agriculture. Consequently, in the city all sorts of things were now mixed together: classes, values, roles. Those things and statuses might be separated out into a simpler less mixed-together world. Technically, such a mixture of what is not to be mixed together is called pollution. And the mathematicians and the city planners aimed to purify and make sense where there was once pollution and disorder."