# Superreal number

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In abstract algebra, the superreal numbers are a class of extensions of the real numbers, introduced by H. Garth Dales and W. Hugh Woodin as a generalization of the hyperreal numbers and primarily of interest in non-standard analysis, model theory, and the study of Banach algebras. The field of superreals is itself a subfield of the surreal numbers.

Dales and Woodin's superreals are distinct from the super-real numbers of David O. Tall, which are lexicographically ordered fractions of formal power series over the reals.[1]

## Formal definition

Suppose X is a Tychonoff space, also called a T space, and C(X) is the algebra of continuous real-valued functions on X. Suppose P is a prime ideal in C(X). Then the factor algebra A = C(X)/P is by definition an integral domain which is a real algebra and which can be seen to be totally ordered. The field of fractions F of A is a superreal field if F strictly contains the real numbers ${\displaystyle {\mathbb {R}}}$, so that F is not order isomorphic to ${\displaystyle {\mathbb {R}}}$.

If the prime ideal P is a maximal ideal, then F is a field of hyperreal numbers (Robinson's hyperreals being a very special case).

## References

1. ^ Tall, David (March 1980), "Looking at graphs through infinitesimal microscopes, windows and telescopes" (PDF), Mathematical Gazette, 64 (427): 22–49, doi:10.2307/3615886, JSTOR 3615886