# Completion of a uniform space

$X$

A separated complete uniform space $\widehat{X}$ for which there exists a uniformly-continuous mapping $i : X \rightarrow \widehat{X}$ such that for any uniformly-continuous mapping $f$ from $X$ into a separated complete uniform space $Y$ there exists a unique uniformly-continuous mapping $g : \widehat{X} \rightarrow Y$ with $f = g \circ i$. The subspace $i ( X)$ is dense in $\widehat{X}$ and the image of entourages in $X$ under $i \times i$ are entourages in $i ( X)$; their closures in $\widehat{X} \times \widehat{X}$ constitute a fundamental system of entourages in $\widehat{X}$. If $X$ is separated, then $i$ is injective (this allows one to identify $X$ with $i ( X)$). The separated completion of a subspace $A \subset X$ is isomorphic to the closure of $i ( A) \subset \widehat{X}$. The separated completion of a product of uniform spaces is isomorphic to the product of the separated completions of the spaces occurring as factors in the product.

The proof of the existence of $\widehat{X}$ generalizes in fact Cantor's construction of the set of real numbers from the set of rational numbers.

#### References

 [1] N. Bourbaki, "Elements of mathematics. General topology" , Addison-Wesley (1966) (Translated from French)
How to Cite This Entry:
Completion of a uniform space. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Completion_of_a_uniform_space&oldid=46426
This article was adapted from an original article by M.I. Voitsekhovskii (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article