Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Extension operators on balls and on spaces of finite sets   We study extension operators between spaces $\sigma_n(2^X)$ of subsets of $X$
of cardinality at most $n$. As an application, we show that if $B_H$ is the
unit ball of a nonseparable Hilbert space $H$, equipped with the weak topology,
then, for any $0<\lambda<\mu$, there is no extension operator $T: C(\lambda
B_H)\to C(\mu B_H)$.

6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg