Nematics mathematical and physical aspects proceedings of the NATO Advanced Research Workshop on Defects, Singularities and Patterns in Nematic Liquid Crystals: Mathematical and Physical Aspects, Orsay, France, May 28 - June 1, 1990 - Coron, Jean-Michel, 1956-; Ghidaglia, Jean-Michel; Hélein, Frédéric, 1963- (Kluwer Academic Publishers, 1991)