Lectures given on the 1st Session of the Centro Internazionale Matematico Estivo (C.I.M.E.) held at Monteca- tini Terme, Italy, June 4-12, 1990

Proceedings of a Conference held in Berlin, 15-20 June, 1990

Proceedings of the US-USSR Symposium held in Chicago, June 20-July 14, 1989

Proceedings of an International Workshop held in Salice Terme, Italy, 26-30 September 1988

Proceedings of a Conference held in Nijmegen, The Netherlands, June 19-21, 1989

Proceedings of a Meeting held in Luminy, France, Sept. 18-22, 1989

Problems of Existence and Uniqueness and their Application

Lectures given at the 2nd Session of the Centro Internazionale Matematico Estivo (C.I.M.E.) held at Montecatini Terme, Italy, July 4-12, 1988