Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: The Boundary Value Problem for a Static 2D Klein--Gordon Equation in the
  Infinite Strip and in the Half-Plane
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol