Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Consequences of Dirac Theory of the Positron   According to Dirac's theory of the positron, an electromagnetic field tends
to create pairs of particles which leads to a change of Maxwell's equations in
the vacuum. These changes are calculated in the special case that no real
electrons or positrons are present and the field varies little over a Compton
wavelength.

18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas