English

Ordered trees and the Geode

Combinatorics 2025-07-25 v1

Abstract

In recent work of Wildberger and Rubine, it is shown that the formal power series S\mathbf{S} in the variables t1,t2,t_1,t_2,\dots satisfying S=1+n1tnSn\mathbf{S}=1+\sum_{n\geq 1} t_n\mathbf{S}^n has a factorisation S=1+(t1+t2+)G\mathbf{S}=1+(t_1+t_2+\cdots)\mathbf{G}, where G\mathbf{G} is a power series with nonnegative coefficients called the Geode. In this note we give a combinatorial interpretation for the coefficients of G\mathbf{G} based on ordered trees. This amends the statement of a disproved conjecture of Wildberger and Rubine which suggests a similar (but incorrect) interpretation.

Keywords

Cite

@article{arxiv.2507.18097,
  title  = {Ordered trees and the Geode},
  author = {Fern Gossow},
  journal= {arXiv preprint arXiv:2507.18097},
  year   = {2025}
}

Comments

7 pages, comments welcome

R2 v1 2026-07-01T04:16:26.523Z