1. [A] F. Angelini,Rappresentazioni di un gruppo libero associate ad una passeggiata a caso, Undergraduate thesis, University of Rome I, 1989.
2. [Boz] M. Bożejko,Uniformly bounded representations of free groups, Journal für die reine und angewandte Mathematik377 (1987), 170–186.
3. [C.S.] M. Cowling and T. Steger,Irreducibility of restrictions of unitary representations to lattices, Journal für die reine und angewandte Mathematik420 (1991), 85–98.
4. [DM-F-T] L. De Michele and A. Figà-TalamancaPositive definite functions on free groups, American Journal of Mathematics102 (1980), 503–509.
5. [F-T-P1] A. Figà-Talamanca and A. M. Picardello,Spherical functions and harmonic analysis on free groups, Journal of Functional Analysis47 (1982), 281–304.