The art of computer programming, volume 3: (2nd ed.) sorting and searching
The art of computer programming, volume 3: (2nd ed.) sorting and searching
Permutations with Restricted Patterns and Dyck Paths
Advances in Applied Mathematics
A bijection between ordered trees and 2-Motzkin paths and its many consequences
Discrete Mathematics
A Construction for Enumerating k-coloured Motzkin Paths
COCOON '95 Proceedings of the First Annual International Conference on Computing and Combinatorics
Enumerative Combinatorics: Volume 1
Enumerative Combinatorics: Volume 1
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A leaf of a plane tree is called an old leaf if it is the leftmost child of its parent, and it is called a young leaf otherwise. In this paper we enumerate plane trees with given numbers of old leaves and young leaves. The formula is obtained combinatorially via two bijections between plane trees and 2-Motzkin paths which map young leaves to red horizontal steps, and old leaves to up steps. We derive some implications for the enumeration of restricted permutations with respect to certain statistics such as pairs of consecutive deficiencies, double descents, and ascending runs. Finally, our main bijection is applied to obtain refinements of two identities of Coker, involving refined Narayana numbers and the Catalan numbers.