Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: 3+1 description of silent universes: a uniqueness result for the Petrov
  type I vacuum case
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg