Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: A theorem on the photographic process in Special Relativity. The train
  paradox revisited
16
The categories of this paper are: stat
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn