2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54845Talks given at the workshop ``Frontiers in Quantum Field Theory'', held in Urumqi, Xinjiang Uygur Autonomous Region, People's Republic of China, 11-19 August 1996.26 pages plain tex with eps diagramsHigh Energy Physics - Theorytext