Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exact solutions in two-dimensional metric $f(R)$-gravity   In this paper we consider the two-dimensional metric $f(R)$-gravity model for
the metric tensor depending on two variable: time and one spacelike coordinate.
We obtain exact analytical vacuum solutions for different forms of function $
f(R) $ which are solutions of cosmological type. These solutions are expressed
in terms of arbitrary functions, which, under certain conditions, can be chosen
as new variables.

25
The categories of this paper are: patt-sol
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The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
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The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
4
The categories of this paper are: cond-mat
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org