Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quasi-local black hole horizons   This article introduces the subject of quasi-local horizons at a level
suitable for physics graduate students who have taken a first course on general
relativity. It reviews properties of trapped surfaces and trapped regions in
some simple examples, general properties of trapped surfaces including their
stability properties, the definitions and some applications of dynamical-,
trapping-, and isolated-horizons.

11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th