Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Kerr-Schild metrics revisited I. The ground state
33
The categories of this paper are: plasm-ph
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg