Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Long-term X-ray variability of quasars in the Lockman Hole field
  observed with ROSAT
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
33
The categories of this paper are: plasm-ph