Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A categorical proof of the Parshin reciprocity laws on algebraic
  surfaces   We define and study the 2-category of torsors over a Picard groupoid, a
central extension of a group by a Picard groupoid, and commutator maps in this
central extension. Using it in the context of two-dimensional local fields and
two-dimensional adelic theory we obtain the two-dimensional tame symbol and a
new proof of Parshin reciprocity laws on an algebraic surface.

12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ