We study almost F-preenvelopes in the category of rings, for a significative class F of commutative rings. We completely identify those rings which have an almost F-preenvelope when F is the class of fields, semisimple rings, integer domains and local rings. We show that rings with Krull dimension zero have (almost) V-preenvelopes, where V is the class of von Neumann regular rings. Mathematics ...

Let Λ be a finite dimensional algebra over an algebraically closed field, and S a finite sequence of simple left Λ-modules. Quasiprojective subvarieties of Grassmannians, distinguished by accessible affine open covers, were introduced by the authors for use in classifying the uniserial representations of Λ having sequence S of consecutive composition factors. Our principal objectives here are t...