D. Friedan, unpublished lectures given at the Mathematics and Physics Conference (Durham, England, July 1979), at the Nuffield Workshop on Quantum Gravity (Cambridge, England, August 13, 1979), and at the Nato Advanced Study Institute on Recent Developments in Gauge Theories (Cargese, France, August 1979), and unpublished manuscript, "Geometric Models for Critical Systems in 2 + ε Dimensions," subtitled "Expanded Version of a talk given at the Nuffield Workshop on Quantum Gravity, DAMTP, Cambridge University, August 13, 1979," commissioned by the directors of the 1979 Nuffield Workshop, and privately circulated to them at the conclusion of the workshop. See also arXiv:hep-ph/0204131.
