Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Charm production at HERA   The ZEUS data on the charm structure function F_2^c at small x fit well to a
single power of x, corresponding to the exchange of a hard pomeron that is
flavour-blind. When combined with the contribution from the exchange of a soft
pomeron, the hard pomeron gives a good description of elastic $J/\psi$
photoproduction.

4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
30
The categories of this paper are: q-alg