Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Interpretation of $\pi N \to \pi \pi N$ Data near Threshold   Near threshold pion production experiments have been recently carried out and
used to extract S--wave $\pi\pi$ scattering lengths. We emphasize here that at
present these processes are related only at the tree level (and its first
correction) in chiral perturbation theory. Higher order corrections (including
loops) must be evaluated before rigorous claims concerning S--wave $\pi\pi$
scattering lengths can be made.

33
The categories of this paper are: plasm-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex