Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Transverse-momentum-dependent parton distributions (TMDs)   Transverse-momentum-dependent parton distributions (TMDs) provide
three-dimensional images of the partonic structure of the nucleon in momentum
space. We made impressive progress in understanding TMDs, both from the
theoretical and experimental point of view. This brief overview on TMDs is
divided in two parts: in the first, an essential list of achievements is
presented. In the second, a selection of open questions is discussed.

15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
22
The categories of this paper are: chao-dyn