Topologizing UCTs for unital extensions

In this paper, we study the topological structure on Ext-groups of unital extensions. It is proved that the stable strong Ext-group and the stable weak Ext-group for unital extensions are pseudopolish groups if A is a unital C^* -algebra in the bootstrap class 𝒩 and B is a stable separable C^* -algebra. Furthermore, we topologize certain UCTs and prove that these UCTs are exact sequences as topological groups.