Non-Contiguous Pattern Avoidance in Binary Trees

@article{Dairyko2012NonContiguousPA,
  title={Non-Contiguous Pattern Avoidance in Binary Trees},
  author={Michael Dairyko and Lara K. Pudwell and Samantha Tyner and Casey Wynn},
  journal={Electron. J. Comb.},
  year={2012},
  volume={19},
  pages={22}
}
In this paper we consider the enumeration of binary trees avoiding non-contiguous binary tree patterns. We begin by computing closed formulas for the number of trees avoiding a single binary tree pattern with 4 or fewer leaves and compare these results to analogous work for contiguous tree patterns. Next, we give an explicit generating function that counts binary trees avoiding a single non-contiguous tree pattern according to number of leaves and show that there is exactly one Wilf class of k… 
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