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arXiv · 2605.10926

Counting Spinal Tree-Child Networks via Word Encodings and Generating Functions

Pau Vives·Anna de Mier·Gabriel Cardona·Joan Carles Pons
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Abstract

We study the enumeration of spinal tree-child phylogenetic networks, a rigid family of tree-child networks in which all internal vertices lie on a single root--to--leaf path. We provide two complementary combinatorial frameworks. First, we introduce a word model: unlabeled spinal networks correspond to a suitable class of restricted words with fixed multiplicities, taken modulo a simple relabeling equivalence, which yields an explicit closed enumeration. Second, we develop a symbolic-method approach based on a marked version of trees that admits a clean recursive specification; its boxed-product translation leads to a solvable bivariate generating function and a direct derivation of the coefficients.

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Pau Vives, Anna de Mier, Gabriel Cardona, Joan Carles Pons. 2026-05-11. Counting Spinal Tree-Child Networks via Word Encodings and Generating Functions. https://arxiv.org/abs/2605.10926

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