Operator Algebras Associated with Free Products of Groups with Amalgamation. Erik Bédos (1984) Mathematische Annalen
Operator k-theory for the group SU(n, 1). Pierre Julg, Gennadi Kasparov (1995) Journal für die reine und angewandte Mathematik
Operators of Finite Rank in Unitary Representations of Exponential Lie Groups. Detlev Poguntke (1982) Mathematische Annalen
Operator-Valued Positive Definite Kernels on Tubes. Karl-Hermann Neeb (1998) Monatshefte für Mathematik