-density, -adic completion and -subgeneration
Let be a ring. We recall that is called a near pseudo-valuation ring if every minimal prime ideal of is strongly prime. Let now be an automorphism of and a -derivation of . Then is said to be an almost -divided ring if every minimal prime ideal of is -divided. Let be a Noetherian ring which is also an algebra over ( is the field of rational numbers). Let be an automorphism of such that is a -ring and a -derivation of such that for all . Further, if for any...
We study the class of modules which are invariant under idempotents of their envelopes. We say that a module M is -idempotent-invariant if there exists an -envelope u : M → X such that for any idempotent g ∈ End(X) there exists an endomorphism f : M → M such that uf = gu. The properties of this class of modules are discussed. We prove that M is -idempotent-invariant if and only if for every decomposition , we have . Moreover, some generalizations of -idempotent-invariant modules are considered....
We prove new necessary and sufficient conditions for a morphism of coalgebras to be a monomorphism, different from the ones already available in the literature. More precisely, φ: C → D is a monomorphism of coalgebras if and only if the first cohomology groups of the coalgebras C and D coincide if and only if for all . In particular, necessary and sufficient conditions for a Hopf algebra map to be a monomorphism are given.
The so-called “invariance under twisting” for twisted tensor products of algebras is a result stating that, if we start with a twisted tensor product, under certain circumstances we can “deform” the twisting map and we obtain a new twisted tensor product, isomorphic to the given one. It was proved before that a number of independent and previously unrelated results from Hopf algebra theory are particular cases of this theorem. In this article we show that some more results from literature are particular...