Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: INTRODUCTION TO THE POMERON STRUCTURE FUNCTION   In many ways the pomeron is like the photon, but there are important
differences. Factorisation allows us to define a pomeron structure function,
even though the pomeron is not a particle. Although we have a model for the
light-quark content of the pomeron, which led to the prediction that a
surprisingly large fraction of events at HERA would have an extremely-fast
final-state proton, its charm and gluon content will have to be got from
experiment. Because the pomeron is not a particle, we cannot derive a momentum
sum rule.

5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
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The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
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The categories of this paper are: cs
18
The categories of this paper are: econ
19
The categories of this paper are: eess
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The categories of this paper are: cond-mat
29
The categories of this paper are: funct-an
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The categories of this paper are: q-fin