Operations on G-sets and the Dress map
Abstract
We study versions of binomial and multichoose coefficients for finite G-sets, extending a result of Siebeneicher from the 1970s concerning the duality between these operations. If the group G comes from a finite Galois extension of fields, the Dress map provides a bridge from G-sets to quadratic forms over the base field. We show that this Dress map is compatible with binomial coefficients of finite G-sets and a particular operation on quadratic forms we define. This allows us to extend the definition of Brugallé and Wickelgren's quadratically enriched binomial coefficients to arbitrary Grothendieck--Witt classes. This allows for a new proof that quadratically enriched binomial coefficients depend only on the trace form of the inputted étale algebra, as well as an elegant reproof of a result of Chen and Wickelgren about binomial coefficients over finite fields.
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BibTeX
@misc{brazelton2026operations,
title = {{Operations on $G$-sets and the Dress map}},
author = {Thomas Brazelton and Ben Spitz},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.23758},
eprint = {2610.23758},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.23758},
}
RIS
TY - UNPB
TI - Operations on G-sets and the Dress map
AU - Thomas Brazelton
AU - Ben Spitz
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2610.23758
UR - https://arxiv.org/abs/2610.23758
AB - We study versions of binomial and multichoose coefficients for finite G-sets, extending a result of Siebeneicher from the 1970s concerning the duality between these operations. If the group G comes from a finite Galois extension of fields, the Dress map provides a bridge from G-sets to quadratic forms over the base field. We show that this Dress map is compatible with binomial coefficients of finite G-sets and a particular operation on quadratic forms we define. This allows us to extend the definition of Brugallé and Wickelgren's quadratically enriched binomial coefficients to arbitrary Grothendieck--Witt classes. This allows for a new proof that quadratically enriched binomial coefficients depend only on the trace form of the inputted étale algebra, as well as an elegant reproof of a result of Chen and Wickelgren about binomial coefficients over finite fields.
ER -