Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Pionium in the elementary particle decays
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol