 It would be out of place in this entry to attempt even a small survey of the developments mentioned above. We simply refer to the reader to Ehrlich (1994) and (2006). The interconnection with many important related issues such as Conway’s surreal numbers (see section  3.4.3)  and other alternative approaches to the construction of the real numbers, such as smooth infinitesimal analysis mentioned at the end of section  3.4.2,  cannot be properly addressed here. See Salanskis and Sinaceur (1992), Ehrlich (1994), Berger, Osswald, and Schuster (2001), and Ehrlich (2012).