R. F. Williams
Purdue University, Lafayette, USA
TBD
mathscidoc:1701.331179
A. D. Michal
California Institute of Technology, Califorina, USA
D. H. Hyers
University of Southern California, Califorina, USA
TBD
mathscidoc:1701.331081
Robert Fricke
Braunschweig
TBD
mathscidoc:1701.33753