Applied Categorical Structures

, Volume 24, Issue 5, pp 619–647 | Cite as

Generalizations of the Sweedler Dual

  • Hans-E. Porst
  • Ross Street


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.


Hopf algebra Coalgebra Sweedler dual Finite dual coalgebra Monoidal functor 

Mathematics Subject Classification (2010)

Primary 16T15 Secondary 18D10 


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© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  1. 1.Department of Mathematical SciencesUniversity of StellenboschStellenboschSouth Africa
  2. 2.Department of MathematicsUniversity of BremenBremenGermany
  3. 3.Centre of Australian Category Theory, Department of MathematicsMacquarie UniversitySydneyAustralia

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