Operations on $G$-sets and the Dress map

Thomas Brazelton; Ben Spitz

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arXiv · 2610.23758

Operations on $G$-sets and the Dress map

Thomas Brazelton·Ben Spitz

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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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Thomas Brazelton, Ben Spitz. 2026-10-16. Operations on $G$-sets and the Dress map. https://arxiv.org/abs/2610.23758

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