Hopf algebras, Steinberg modules, and the unstable cohomology of SL_n(mathbb Z) and GL_n(mathbb Z)
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We prove that the direct sum of all homology groups of the integral general linear groups with Steinberg module coefficients form a commutative Hopf algebra, in particular a free graded commutative algebra. We use this to construct new infinite families of unstable cohomology classes of $SL_n(\mathbb Z)$.
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Cited by 3 Pith papers
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A projective resolution of the symplectic Steinberg module
Constructs a projective resolution of the symplectic Steinberg module St^ω_{2n}(K) for Sp_{2n}(R), analogous but more involved than Lee-Szczarba's for SL_n, and applies it to compute top cohomology of principal level-...
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A projective resolution of the symplectic Steinberg module
Constructs a projective resolution of the symplectic Steinberg module St^ω_{2n}(K) and uses it to compute top cohomology of level-p congruence subgroups of Sp_{2n}(R) for Euclidean R with surjective unit map.
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