Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Riordan Groups in $d$ Dimensions   The classical Riordan groups associated to a given commutative ring are
groups of infinite matrices (called Riordan arrays) associated to pairs of
formal power series in one variable. The Fundamental Theorem of Riordan Arrays
relates matrix multiplication to two group actions on such series, namely
formal (convolution) multiplication and formal composition. We define the
analogous Riordan groups involving formal power series in several variables,
and establish the analogue of the Fundamental Theorem in that context.

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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: supr-con
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The categories of this paper are: q-alg
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The categories of this paper are: hep-lat
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The categories of this paper are: q-bio
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: eess
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The categories of this paper are: ao-sci
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The categories of this paper are: econ
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The categories of this paper are: cond-mat
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-ex