Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Derivation of Source-Free Maxwell and Gravitational Radiation Equations
  by Group Theoretical Methods
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
18
The categories of this paper are: econ
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int