Second International Conference, Symmetry in Nonlinear Mathematical Physics, Vol I (Institute of Mathematics of the National Academy of Sciences of Ukraine, Kiev, 1997) 21-33. See also Kent Harrison, Remarks for Closing Ceremony, Vol. 2, 499
Remarks on Integrability Conditions and Backlund Transformations for Vacuum Einstein Equations
Solutions of Einstein's Equations: Techniques and Results, Proc. International Seminar on Exact Solutions of Einstein's Equations, Retzbach, Germany, Nov. 1983.
Lecture Notes in Phys. 205, 26-54 (1984).