On Numbers and Games

{{Short description|1976 mathematics book by John Conway}}

{{infobox book

| name = On Numbers and Games

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| image = On Numbers and Games.jpg

| caption = First edition

| author = John Horton Conway

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| country = United States

| language = English

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| genre = Mathematics

| publisher = Academic Press, Inc.

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| media_type = Print

| pages = 238 pp.

| isbn = 0-12-186350-6

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On Numbers and Games is a mathematics book by John Horton Conway first published in 1976.{{cite journal|author=Fraenkel, Aviezri S.|author-link=Aviezri Fraenkel|title=Review: On numbers and games, by J. H. Conway; and Surreal numbers, by D. E. Knuth|journal=Bull. Amer. Math. Soc.|year=1978|volume=84|issue=6|pages=1328–1336|url=https://www.ams.org/journals/bull/1978-84-06/S0002-9904-1978-14564-9/S0002-9904-1978-14564-9.pdf|doi=10.1090/s0002-9904-1978-14564-9|doi-access=free}} The book is written by a pre-eminent mathematician, and is directed at other mathematicians. The material is, however, developed in a playful and unpretentious manner and many chapters are accessible to non-mathematicians. Martin Gardner discussed the book at length, particularly Conway's construction of surreal numbers, in his Mathematical Games column in Scientific American in September 1976.{{cite magazine |first=Martin |last=Gardner |url=http://www.scientificamerican.com/article/mathematical-games-1976-09/ |title=Mathematical Games |date=September 1976 |magazine=Scientific American |volume=235 |issue=3}}

The book is roughly divided into two sections: the first half (or Zeroth Part), on numbers, the second half (or First Part), on games. In the Zeroth Part, Conway provides axioms for arithmetic: addition, subtraction, multiplication, division and inequality. This allows an axiomatic construction of numbers and ordinal arithmetic, namely, the integers, reals, the countable infinity, and entire towers of infinite ordinals. The object to which these axioms apply takes the form {L|R}, which can be interpreted as a specialized kind of set; a kind of two-sided set. By insisting that LDedekind cut. The resulting construction yields a field, now called the surreal numbers. The ordinals are embedded in this field. The construction is rooted in axiomatic set theory, and is closely related to the Zermelo–Fraenkel axioms. In the original book, Conway simply refers to this field as "the numbers". The term "surreal numbers" is adopted later, at the suggestion of Donald Knuth.

In the First Part, Conway notes that, by dropping the constraint that Lclass of all two-player games. The axioms for greater than and less than are seen to be a natural ordering on games, corresponding to which of the two players may win. The remainder of the book is devoted to exploring a number of different (non-traditional, mathematically inspired) two-player games, such as nim, hackenbush, and the map-coloring games col and snort. The development includes their scoring, a review of the Sprague–Grundy theorem, and the inter-relationships to numbers, including their relationship to infinitesimals.

The book was first published by Academic Press in 1976, {{isbn|0-12-186350-6}}, and a second edition was released by A K Peters in 2001 ({{isbn|1-56881-127-6}}).