Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Self-adjoint Extensions for Confined Electrons:from a Particle in a
  Spherical Cavity to the Hydrogen Atom in a Sphere and on a Cone
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
9
The categories of this paper are: nlin