Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological invariants of time reversal invariant superconductors   The topological invariants of gapped time reversal invariant lattice
superconductors are studied by mapping the superconducting mean field
Hamiltonian to a Bloch Hamiltonian. There is a single $Z_2 $ invariant in two
dimensions and four such invariants in three dimensions. We briefly discuss the
properties of states with non-trivial topological invariants.

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The categories of this paper are: q-bio
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
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The categories of this paper are: comp-gas
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The categories of this paper are: adap-org
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-lat
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The categories of this paper are: alg-geom
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The categories of this paper are: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: atom-ph
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The categories of this paper are: physics
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The categories of this paper are: math-ph