Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the covariant formulation of Dirac's equation   As a continuation of previous investigations, the formalism used there is
extended to the case when an external electric field is present and the
covariant formulation is performed again. The equation system obtained allows
no restriction in the manifold of the quantities if an undesired
overdetermination is to be avoided. The combined appearance of the dual
formations also indicates an improbable internal properly of the system and
suggests that the underlying Dirac equation needs a modification. (Editorial
note: In this paper Lanczos continues to discuss his ``fundamental equation,''
from which two Dirac fields forming an isospin doublet, or two spin 1 fields of
opposite parities, derive.)

31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
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The categories of this paper are: stat
8
The categories of this paper are: hep-ex
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The categories of this paper are: q-fin
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The categories of this paper are: quant-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex