Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Analytical Description of Voids in Majumdar-Papapetrou Spacetimes   We discuss new Majumdar-Papapetrou solutions for the 3+1 Einstein-Maxwell
equations, with charged dust acting as the external source of the fields. The
solutions satisfy non-linear potential equations which are related to
well-known wave equations of 1+1 soliton physics. Although the matter
distributions are not localised, they present central structures which may be
identified with voids.

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The categories of this paper are: mtrl-th
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The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
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The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: stat
6
The categories of this paper are: astro-ph
18
The categories of this paper are: econ