Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Plane waves in a general Robertson-Walker background
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con