Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Commutators cannot be proper powers in metric small-cancellation
  torsion-free groups   A nontrivial commutator cannot be a proper power in a torsion-free group
satisfying C'(\lambda) small cancellation condition with sufficiently small
\lambda.

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The categories of this paper are: acc-phys
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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-th
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The categories of this paper are: cond-mat
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: stat
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The categories of this paper are: hep-ph
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an