A combinatorial proof of Postnikov's identity and a generalized enumeration of labeled trees
arXiv:math/0409323
Abstract
In this paper, we give a simple combinatorial explanation of a formula of A. Postnikov relating bicolored rooted trees to bicolored binary trees. We also present generalized formulas for the number of labeled k-ary trees, rooted labeled trees, and labeled plane trees.
9 pages, 3 figures (use PSTricks)