Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On Fermat's principle for causal curves in time oriented Finsler
  spacetimes   In this work, a version of Fermat's principle for causal curves with the same
energy in time orientable Finsler spacetimes is proved. We calculate the
secondvariation of the {\it time arrival functional} along a geodesic in terms
of the index form associated with the Finsler spacetime Lagrangian. Then the
character of the critical points of the time arrival functional is investigated
and a Morse index theorem in the context of Finsler spacetime is presented.

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The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
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The categories of this paper are: eess
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The categories of this paper are: patt-sol
18
The categories of this paper are: econ
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
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The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph
4
The categories of this paper are: cond-mat
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The categories of this paper are: supr-con
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: q-fin
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The categories of this paper are: comp-gas