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Distribution of crossings, nestings and alignments of two edges in matchings and partitions. (English) Zbl 1096.05006
Summary: We construct an involution on set partitions which keeps track of the numbers of crossings, nestings and alignments of two edges. We derive then the symmetric distribution of the numbers of crossings and nestings in partitions, which generalizes a recent result of Klazar and Noy on perfect matchings. By factorizing our involution through bijections between set partitions and some path diagrams we obtain the continued fraction expansions of the corresponding ordinary generating functions.

05A18 Partitions of sets
05A15 Exact enumeration problems, generating functions
05A30 \(q\)-calculus and related topics
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