Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Unusual formations of the free electromagnetic field in vacuum
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga