Shuffle of parenthesis systems and Baxter permutations
Journal of Combinatorial Theory Series A
Enumerative combinatorics
On the structure of the lattice of noncrossing partitions
Discrete Mathematics
The lattice of non-crossing partitions and the Birkhoff-Lewis equations
European Journal of Combinatorics
Chains in the lattice of noncrossing partitions
Discrete Mathematics
Combinatorics of generalized q-Euler numbers
Journal of Combinatorial Theory Series A
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We consider two combinatorial statistics on permutations. One isthe genus. The other, \widehat{\rm des}, is defined for alternating permutations, as the sum of the number of descents in thesubwords formed by the peaks and the valleys. We investigatethe distribution of des on genus zero permutations and Baxterpermutations. Our q-enumerative results relate the des statistic to lattice path enumeration, the rank generating function andcharacteristic polynomial of noncrossing partition lattices,and polytopes obtained as face-figures of the associahedron.