Abstract
As left adjoint to the dual algebra functor, Sweedler’s finite dual construction is an important tool in the theory of Hopf algebras over a field. We show in this note that the left adjoint to the dual algebra functor, which exists over arbitrary rings, shares a number of properties with the finite dual. Nonetheless the requirement that it should map Hopf algebras to Hopf algebras needs the extra assumption that this left adjoint should map an algebra into its linear dual. We identify a condition guaranteeing that Sweedler’s construction works when generalized to noetherian commutative rings. We establish the following two apparently previously unnoticed dual adjunctions: For every commutative ring R the left adjoint of the dual algebra functor on the category of R-bialgebras has a right adjoint. This dual adjunction can be restricted to a dual adjunction on the category of Hopf R-algebras, provided that R is noetherian and absolutely flat.
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To the memory of Horst Herrlich
The second author gratefully acknowledges the support of Australian Research Council Discovery Grant DP130101969.
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Porst, HE., Street, R. Generalizations of the Sweedler Dual. Appl Categor Struct 24, 619–647 (2016). https://doi.org/10.1007/s10485-016-9450-2
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DOI: https://doi.org/10.1007/s10485-016-9450-2