Semigroups of representational indices of derivations of \(C^*\)- algebras (Q1340851)

In the framework of the index theory of derivations of \(C^*\)-algebras, the author introduced the notion of representational index of a derivation in [J. Reine Angew. Math. 439, 71-92 (1993; Zbl 0765.46057), Pac. J. Math. 162, No. 1, 97-120 (1994; Zbl 0792.46050)]. Here he associates two commutative monoids and a commutative group of representational indices with every set of closed *-derivations of a \(C^*\)-algebra implemented by symmetric operators, and gives an explicit description of them in various cases.