Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Mathematical Features of Several Cosmological Models   Einstein equations for several matter sources in homogeneous, isotropic
metric are shown to reduce to a second order nonlinear ordinary differential
equation. An analysis of its solutions is made in an important case.

2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio