where Δ denotes any ternary subtree. Note that u might be the same as ν. Mean-while,a leaf in θ( T) corresponds to an internal vertex in T whose left and middle
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Chapter 6 Noncrossing Trees
subtrees are empty,that is,a pattern
.
Dershowitz and Zaks[Dershowitz et al.,1989] gave the enumeration of pat-
terns