Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On gauge invariance and the path integral   Using a gauge covariant operator technique we deduce the path integral for a
charged particle in a stationary magnetic field, verifying the "midpoint rule"
for the discrete form of the interaction term with the vector potential.

35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
25
The categories of this paper are: patt-sol
1
The categories of this paper are: cs
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
18
The categories of this paper are: econ
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph