Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Version of Thirring's Approach to the KAM Theorem for Quadratic
  Hamiltonians with Degenerate Twist   We give a proof of the KAM theorem on the existence of invariant tori for
weakly perturbed Hamiltonian systems, based on Thirring's approach for
Hamiltonians that are quadratic in the action variables. The main point of this
approach is that the iteration of canonical transformations on which the proof
is based stays within the space of quadratic Hamiltonians. We show that
Thirring's proof for nondegenerate Hamiltonians can be adapted to Hamiltonians
with degenerate twist. This case, in fact, drastically simplifies Thirring's
proof.

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The categories of this paper are: funct-an
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: astro-ph
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The categories of this paper are: cs
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The categories of this paper are: econ
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The categories of this paper are: hep-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph
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The categories of this paper are: q-alg
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: cond-mat
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The categories of this paper are: alg-geom