Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the boundary of the region containing trapped surfaces   The boundary of the region in spacetime containing future-trapped closed
surfaces is considered. In asymptotically flat spacetimes, this boundary does
not need to be the event horizon nor a dynamical/trapping horizon. Some
properties of this boundary and its localization are analyzed, and illustrated
with examples. In particular, fully explicit future-trapped compact surfaces
penetrating into flat portions of a Vaidya spacetime are presented.

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The categories of this paper are: econ
23
The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: nlin
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-th
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The categories of this paper are: q-alg
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: cmp-lg