Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Two-Dimensional Time-Reversal-Invariant Topological Insulators via
  Fredholm Theory
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th