Noncommutative Abel-like identities
Abstract
We generalize the Abel--Hurwitz identities to an almost entirely noncommutative setting. Namely, let be a finite set of size , and let be any noncommutative ring. For each , let . Set for any . Let and be two elements of such that lies in the center of . Then, we show that% \begin{align*} & \sum_{S\subseteq V}\left( X+x\left( S\right) \right) ^{\left\vert S\right\vert }\left( Y-x\left( S\right) \right) ^{n-\left\vert S\right\vert }=\sum_{\substack{i_{1},i_{2},\ldots,i_{k}\in V\text{ distinct}% }}\left( X+Y\right) ^{n-k}x_{i_{1}}x_{i_{2}}\cdots x_{i_{k}};\\ & \sum_{S\subseteq V}X\left( X+x\left( S\right) \right) ^{\left\vert S\right\vert -1}\left( Y-x\left( S\right) \right) ^{n-\left\vert S\right\vert }=\left( X+Y\right) ^{n};\\ & \sum_{S\subseteq V}X\left( X+x\left( S\right) \right) ^{\left\vert S\right\vert -1}\left( Y-x\left( S\right) \right) ^{n-\left\vert S\right\vert -1}\left( Y-x\left( V\right) \right) =\left( X+Y-x\left( V\right) \right) \left( X+Y\right) ^{n-1}. \end{align*} (Negative powers are understood to be cancelled by other factors.)
Cite
@article{arxiv.2604.12619,
title = {Noncommutative Abel-like identities},
author = {Darij Grinberg},
journal= {arXiv preprint arXiv:2604.12619},
year = {2026}
}
Comments
21 pages. Preprint from 2017, with minor corrections. Applications and other comments welcome!