A Relationship between Hnn Extensions and Amalgamated Free Products in Operator Algebras
نویسندگان
چکیده
By improving the previous construction in [18] we observe that any reduced HNN extension is a corner of a certain reduced amalgamated free product in both the von Neumann algebra and the C∗-algebra settings. Then, the same fact is shown for universal HNN extensions of C∗-algebras. We apply the observation to the questions of factoriality and type classification of HNN extensions of von Neumann algebras and also those of simplicity and K-theory of (reduced and/or universal) HNN extensions of C∗-algebras.
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