TITLE: Approximation theorems
QUESTION [14 upvotes]: The Weierstrass' approximation theorem for continuous functions on a compact space by using polynomials is well-known. As far as I know, there are some variants of this theorem, e.g. Stone-Weierstrass that refers not only to polynomials as approximator functions. Where could I find these Weierstrass-like approximation theorems? On-line references are OK, but one might also point to some books.
Thanks in advance,
Lucian

REPLY [2 votes]: If you want some technical challenge (or let's say, it really is for me) you can have a look at A. Pinkus. N-widths in Approximation Theory, Springer-Verlag, New York, 1980.