Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Huygens' principle and Dirac-Weyl equation   We investigate the validity of Huygens' principle for forward propagation in
the massless Dirac-Weyl equation. The principle holds for odd space dimension
n, while it is invalid for even n. We explicitly solve the cases n=1,2 and 3
and discuss generic $n$. We compare with the massless Klein-Gordon equation and
comment on possible generalizations and applications.

17
The categories of this paper are: q-fin
6
The categories of this paper are: astro-ph
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ