No Arabic abstract
Let R be a local domain, v a valuation of its quotient field centred in R at its maximal ideal. We investigate the relationship between R^h, the henselisation of R as local ring, and {~v}, the henselisation of the valuation v, by focussing on the recent result by de Felipe and Teissier referred to in the title. We give a new proof that simplifies the original one by using purely algebraic arguments. This proof is moreover constructive in the sense of Bishop and previous work of the authors, and allows us to obtain as a by-product a (slight) generalisation of the theorem by de Felipe and Teissier.
In the recent paper Mutation in triangulated categories and rigid Cohen-Macaulay modules Iyama and Yoshino consider two interesting examples of isolated singularities over which it is possible to classify the indecomposable maximal Cohen-Macaulay modules in terms of linear algebra data. In this paper we present two new approaches to these examples. In the first approach we give a relation with cluster categories. In the second approach we use Orlovs result on the graded singularity category. We obtain some new results on the singularity category of isolated singularities which may be interesting in their own right.
We develop new methods to study $mathfrak{m}$-adic stability in an arbitrary Noetherian local ring. These techniques are used to prove results about the behavior of Hilbert-Samuel and Hilbert-Kunz multiplicities under fine $mathfrak{m}$-adic perturbations.
The main aim of this article is to study the relation between $F$-injective singularity and the Frobenius closure of parameter ideals in Noetherian rings of positive characteristic. The paper consists of the following themes, including many other topics. We prove that if every parameter ideal of a Noetherian local ring of prime characteristic $p>0$ is Frobenius closed, then it is $F$-injective. We prove a necessary and sufficient condition for the injectivity of the Frobenius action on $H^i_{fm}(R)$ for all $i le f_{fm}(R)$, where $f_{fm}(R)$ is the finiteness dimension of $R$. As applications, we prove the following results. (a) If the ring is $F$-injective, then every ideal generated by a filter regular sequence, whose length is equal to the finiteness dimension of the ring, is Frobenius closed. It is a generalization of a recent result of Ma and which is stated for generalized Cohen-Macaulay local rings. (b) Let $(R,fm,k)$ be a generalized Cohen-Macaulay ring of characteristic $p>0$. If the Frobenius action is injective on the local cohomology $H_{fm}^i(R)$ for all $i < dim R$, then $R$ is Buchsbaum. This gives an answer to a question of Takagi. We consider the problem when the union of two $F$-injective closed subschemes of a Noetherian $mathbb{F}_p$-scheme is $F$-injective. Using this idea, we construct an $F$-injective local ring $R$ such that $R$ has a parameter ideal that is not Frobenius closed. This result adds a new member to the family of $F$-singularities. We give the first ideal-theoretic characterization of $F$-injectivity in terms the Frobenius closure and the limit closure. We also give an answer to the question about when the Frobenius action on the top local cohomology is injective.
We give an elementary proof of Grothendiecks non-vanishing Theorem: For a finitely generated non-zero module $M$ over a Noetherian local ring $A$ with maximal ideal $m$, the local cohomology module $H^{dim M}_{m}(M)$ is non-zero.
We prove a duality theorem for graded algebras over a field that implies several known duality results : graded local dualit