Recursive tree

Summary

In graph theory, a recursive tree (i.e., unordered tree) is a labeled, rooted tree. A size-$n$ recursive tree's vertices are labeled by distinct positive integers $1, 2, \ldots, n$, where the labels are strictly increasing starting at the root labeled 1. Recursive trees are non-planar, which means that the children of a particular vertex are not ordered; for example, the following two size-3 recursive trees are equivalent: ${}_{3}/^{1}\backslash_{2} =_{2}/^{1}\backslash_{3}$.