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On \({\mathbb{P}}\)-morphisms and openness of loci. (English) Zbl 0618.13003

All rings are assumed to be commutative with unit and noetherian. Let \({\mathbb{P}}\) be a property which makes sense for noetherian local rings, e.g. regular, normal, reduced, Cohen-Macaulay, \((S_ n)\), \((R_ n)\) etc. For properties \({\mathbb{P}}\) verifying some list of axioms, and which do not verify all usual axioms (e.g. \((R_ n)\), \((T_ n)\) etc.), the author gives answers, under very general and natural assumptions, to a problem of Rotthaus about lifting of openness of \({\mathbb{P}}\)-loci and to a question of Valabrega about a useful criterion for \({\mathbb{P}}\)-morphisms.
Reviewer: I.Crivei

MSC:

13B99 Commutative ring extensions and related topics
13H99 Local rings and semilocal rings
13B02 Extension theory of commutative rings