Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Density in Approximation Theory   Approximation theory is concerned with the ability to approximate functions
by simpler and more easily calculated functions. The first question we ask in
approximation theory concerns the {\it possibility of approximation}. Is the
given family of functions from which we plan to approximate dense in the set of
functions we wish to approximate? In this work we survey some of the main
density results and density methods.

13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics