2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/228454For homomorphism K-->S of commutative rings, where K is Gorenstein and S is essentially of finite type and flat as a K-module, the property that all non-trivial fiber rings of K-->S are Gorenstein is characterized in terms of properties of the cohomology modules Ext_n^{S\otimes_KS}S{S\otimes_KS}.This is the published version, except for updates to references and bibliography. Sections 3, 4 and 8 have been removed from the preceding version, arXiv:0704.3761v2. Substantial generalizations of results in those sections are proved in our paper with Joseph Lipman and Suresh Nayak, arXiv:0904.4004Commutative AlgebraRings and Algebras13D03, 14B25 (Primary) 14M05, 16E40 (Secondary)text