Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Note on aligned Petrov type D purely magnetic perfect fluids   We recently showed (Class. Quantum Grav.\ 23, 3353; gr-qc/0602091) that
aligned Petrov type D purely magnetic perfect fluids are necessarily locally
rotationally symmetric (LRS) and hence are all explicitly known. We provide
here a more transparent proof.

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The categories of this paper are: acc-phys
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The categories of this paper are: mtrl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: math-ph
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The categories of this paper are: q-alg
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The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: astro-ph
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The categories of this paper are: q-bio
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org
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The categories of this paper are: solv-int