Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A translation of the paper: On the question of avoiding the infinite
  "self-reaction" of the electron, by V. Ambarzumian and D. Ivanenko (1930)   An attempt is made to avoid the difficulty of the infinite reaction of the
electron on itself, which occurs in quantum electrodynamics, by introducing
difference equations instead of differential equations. This vision allows the
difficulty of the relativistic wave equation emphasised by Klein, for example,
to be essentially eliminated.

15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
2
The categories of this paper are: math