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Published online by Cambridge University Press: 17 December 2012
We show that if $A$ and
$H$ are Hopf algebras that have equivalent tensor categories of comodules, then one can transport what we call a free Yetter–Drinfeld resolution of the counit of
$A$ to the same kind of resolution for the counit of
$H$, exhibiting in this way strong links between the Hochschild homologies of
$A$ and
$H$. This enables us to obtain a finite free resolution of the counit of
$\mathcal {B}(E)$, the Hopf algebra of the bilinear form associated with an invertible matrix
$E$, generalizing an earlier construction of Collins, Härtel and Thom in the orthogonal case
$E=I_n$. It follows that
$\mathcal {B}(E)$ is smooth of dimension 3 and satisfies Poincaré duality. Combining this with results of Vergnioux, it also follows that when
$E$ is an antisymmetric matrix, the
$L^2$-Betti numbers of the associated discrete quantum group all vanish. We also use our resolution to compute the bialgebra cohomology of
$\mathcal {B}(E)$in the cosemisimple case.