Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Helical Fermi arcs and surface states in time-reversal invariant Weyl
  semimetals
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
2
The categories of this paper are: math
3
The categories of this paper are: physics
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin