Total extension groups for unital Kirchberg algebras

We introduce a hierarchy for unital Kirchberg algebras with finitely generated K-groups by which the first and second homotopy groups of the automorphism groups serve as a complete invariant of classification. We also introduce an invariant called the total extension group which is the direct sum of the strong and weak extension groups. In the case of unital Kirchberg algebras with finitely generated K-groups, the total extension group gives a complete invariant and provides a useful tool to classify the Cuntz–Krieger algebras.