Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: The infinite red-shift surfaces of the Kerr and Kerr-Newman solutions of
  the Einstein field equations
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
3
The categories of this paper are: physics
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph