Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the gravitational field of a sphere of incompressible fluid according
  to Einstein's theory   Communication by K. Schwarzschild to the Prussian Academy of Sciences,
dealing with the gravitational field of a sphere of incompressible fluid.

13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph