1998. Force majeure and hardship under the UNIDROIT Principles of International Commercial Contracts, in: Contratación internacional. Comentarios a los Principios sobre los Contratos Comerciales Internacionales del Unidroit, Universidad Nacional Autónoma de México - Universidad Panamericana (1998) 111-133 [SUMMARY: I. Legal Background in the Civil Law and Common Law. II. Contractual usages in International trade. III. The Underpinnings of the Force Majeure and Hardship Excuses. IV. The UNIDROIT Principles]