Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Coulomb Gap in the Density of States of Disordered Metals in Two
  Dimensions
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th