Abstract. We construct Hopf algebra isomorphisms of discrete multiplier Hopf C*-algebras, and Hopf AF C*-algebras (generalized quantum UHF algebras), from K-theoretical data. Some of the intermediate results are of independent interest, such as a result that Jordan maps of Hopf algebras intertwine antipodes, and the applications to automorphisms of Hopf algebras.
IntroductionClassification is a recurring theme in mathematics, and probably the most successful approach to classifying C*-algebras has been to use Ktheory, often augumented by some additional information, as a classifying functor [10]. We consider the case of C*-algebras with Hopf algebra structure, and we find that in many cases there is a product structure on the K-theory group. We then address the problem of constructing Hopf algebra maps from algebra maps respecting the product structure on the K-theory group, with applications to constructing automorphisms and isomorphisms of Hopf algebras. Theorems 2.10, 3.2 and 2.11 allow constructing Hopf algebra (co-anti) automorphisms or isomorphisms from purely K-theoretical data. These results are used to study bi-inner Hopf *-automorphisms, which are the Hopf *-automorphisms of a Hopf C*-algebra that are inner as algebra automorphisms, both in the dual algebra and in the given algebra. We extend the results of [21]. We also develop techniques of independent interest, involving Jordan bi-algebra maps, linear positivity preserving maps, and other related concepts. In the last two sections, we give an example where we apply the techniques to the case of a Hopf AF C*-algebra, which includes an interesting special case that we call the quantum UHF case. With a compact Hopf AF C*-algebra can be associated two K-theory 1991 Mathematics Subject Classification. Primary 47L80, 16T05; Secondary 47L50, 16T20 .