Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Wave propagation in a weak gravitational field and the validity of the
  thin lens approximation
19
The categories of this paper are: eess
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
3
The categories of this paper are: physics