Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Linear confinement in momentum space: singularity-free bound-state
  equations
9
The categories of this paper are: nlin
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas