Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time symmetric electrodynamics, electric charge conservation, and the
  Lorenz gauge   We show how the Lorenz gauge condition is related to the electric charge
conservation, in a universe where electrically charged point particles are
created and annihilated. We derive our results using time symmetric
electrodynamics, relying on observations made by Jacov Frenkel (in 1925) and
John Archibald Wheeler (in 1940).

30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
26
The categories of this paper are: bayes-an
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph