Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Projective Connections and the Algebra of Densities   Projective connections first appeared in Cartan's papers in the 1920's. Since
then they have resurfaced periodically in, for example, integrable systems and
perhaps most recently in the context of so called projectively equivariant
quantisation. We recall the notion of projective connection and describe its
relation with the algebra of densities on a manifold. In particular, we
construct a Laplace-type operator on functions using a Thomas projective
connection and a symmetric contravariant tensor of rank 2 (`upper metric').

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The categories of this paper are: chem-ph
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: stat
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The categories of this paper are: nlin
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-th
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: physics
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: ao-sci
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn