The authors of this report were priviledged to attend this conference, held in the beautiful hamlet of Oberwolfach, nestled in the Black Forest of Southwestern Germany, near Strasbourg, France. The German government sponsors 51 one-week meetings every year (only Christmas week is excluded) in a facility expressly designed for and devoted to meetings of mathematicians. Lodging and (delicious) meals are provided in a pleasant, modern guesthouse. In the adjacent buildings there are meeting rooms, a well equipped library, and recreational facilities such as billiards, table tennis and a music room supplied with enough instruments for a string quartet plus a stein way piano; yet, characteristically, there is no radio and no TV. The whole atmosphere is especially conducive to long leisurely scholarly discussions which, combined with the formal meetings, provide an outstanding opportunity to recharge the mental batteries along the lines of a rather specific mathematical topic. Any mathematically oriented reader who has never attended an Oberwolfach meeting should make every attempt to be invited to one, It will he lpto have a working knowledge of German language, as most of the conferences are conducted principally in that language. In this particular conference, however, most of the papers were presented in English, as a courtesy to the attending non-Germans.