Audio recording of part two of a lecture delivered on in two parts on February 18 and 25, 1972 by Beate Ruhm von Oppen as part of the Formal Lecture Series.
Typescript of a lecture given on September 14, 1973, by Curtis Wilson as part of the Formal Lecture Series. The lecture was also published in The College, volume XXXI, number 2 (January 1980), pages 21-31.