Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the proper choice of a Lorentz-covariant relativistic Lagrangian   A proper choice for the sign of the Lorentz-covariant relativistic Lagrangian
for a particle moving in an electromagnetic field is presented. This choice is
based on which space-time metric is used in the representation of the
relativistic particle dynamics.

9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph