Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 1983 paper on entanglement entropy: "On the Entropy of the Vacuum
  outside a Horizon"   I introduce the concept of *entanglement entropy* (as it's now called) and
point out that it follows an *area law* which renders it a suitable source of
black hole entropy. I also suggest to conceive the latter as residing on the
horizon at approximately one bit per "Planckian plaquette".

11
The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ