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The Quillen and sharbly Hopf algebra structures on Steinberg homology coincide

Urshita Pal, Sam Payne

math.ATarXiv:2609.38735

Abstract

Two recent constructions independently give bigraded commutative Hopf algebra structures on the homology of GL(Z) with rational Steinberg coefficients. One, by Ash--Miller--Patzt, uses the sharbly resolution. The other, by Brown--Chan--Galatius--Payne, uses the Quillen spectral sequence and rank-filtered maps on BK(Z). We prove that the two structures coincide. Both are induced by join and parabolic restriction operations on Steinberg modules.

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