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A bijection between noncrossing and nonnesting partitions of types A, B and C

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Abstract:

The total number of noncrossing partitions of type $Psi$ is the $n$th Catalan number $frac{1}{n+1}inom{2n}{n}$ when $Psi=A_{n-1}$, and the coefficient binomial $inom{2n}{n}$ when $Psi=B_n$ or $C_n$, and these numbers coincide with the correspondent number of nonnesting partitions. For type A, there are several bijective proofs of this equality; in particular, the intuitive map, which locally converts each crossing to a nesting, is one of them. In this paper we present a bijection between nonnesting and noncrossing partitions of types $A, B$ and $C$ that generalizes the type $A$ bijection that locally converts each crossing to a nesting.

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