The title of this talk, given seven days since the last one, and the contents of the lecture itself are essentially repetitions
of two previous lectures with the same title: one given as the Pasquariello Lecture at the Children's Hospital of Philadelphia
on April 8, 1987, and the first given at the Annual Research Dinner in St. Louis, Missouri on April 24, 1987. For reasons
stated in the introductions of the Pasquariello Lecture, just the title sheet will be presented in this archive and there
will be no index.