Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: SWAS and Arecibo observations of H2O and OH in a diffuse cloud along the
  line-of-sight to W51
28
The categories of this paper are: alg-geom
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an