Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The 't Hooft vertex revisited   In 1976 't Hooft introduced an elegant approach towards understanding the
physical consequences of the topological structures that appear in non-Abelian
gauge theories. These effects are concisely summarized in terms of an effective
multi-fermion interaction. These old arguments provide a link between a variety
of recent and sometimes controversial ideas including discrete chiral
symmetries appearing in some models for unification, ambiguities in the
definition of quark masses, and flaws with some simulation algorithms in
lattice gauge theory.

26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph