Much of the material presented in these notes was worked out in
collaboration with K.Kutzler and my former students: H.P.Butzmann, W.A.Feld-
man and M.Schroder. I am greatly indebted to all of them.
Special thanks go to H.P.Butzman and B.Muller for their criticisms,
suggestions and the painful job of proofreading.
The suggestion of C.H.Cook to write these notes in English provided
him and Dany Gulick with some work of linguistic adjustments. I am
grateful to both of them.
The manuscript was typed by Mrs.K.Bischoff. I would Like to thank her
very much for the care she took with this job.