We show that the linked Grassmannian scheme, which arises in a functorial compactification of spaces of limit linear series, and in local models of certain Shimura varieties, is Cohen-Macaulay, reduced, and flat. We give an application to spaces of limit linear series.

For a Noetherian local domain A, there exists an upper bound Nτ (A) on the minimal number of generators of any height two ideal a for whichA/a is Cohen-Macaulay of type τ . If A contains an infinite field, then we may take Nτ (A) := (τ + 1)ehom(A), where ehom(A) is the homological multiplicity of A.

We generalise Yoshino’s definition of a degeneration of two Cohen Macaulay modules to a definition of degeneration between two objects in a triangulated category. We derive some natural properties for the triangulated category and the degeneration under which the Yoshino-style degeneration is equivalent to the degeneration defined by a specific distinguished triangle analogous to Zwara’s charac...

Let A be a noetherian ring which is locally Macaulay. For each integer i ^ O , groups d(A) and Wi(A) are denned, each sequence of groups generalizing to higher dimensions the usual class group of an integrally closed noetherian domain. d(A) is called the ith class group of A, and Wi(A) is called the ith homologuai class group of A. The main purpose of this note is to show that both sequences of...

In an earlier work the authors described a mechanism for lifting monomial ideals to reduced unions of linear varieties. When the monomial ideal is Cohen-Macaulay (including Artinian), the corresponding union of linear varieties is arithmetically CohenMacaulay. The first main result of this paper is that if the monomial ideal is Artinian then the corresponding union is in the Gorenstein linkage ...

We construct a new efficient algorithm for finding Gröbner–Shirshov bases for noncommutative algebras and their representations. This algorithm uses the Macaulay matrix [F.S. Macaulay, On some formula in elimination, Proc. London Math. Soc. 33 (1) (1902) 3–27], and can be viewed as a representation theoretic analogue of the F4 algorithm developed by J.C. Faugère. We work out some examples of un...

In this paper, we introduce the notion of “extension” of a toric variety and study its fundamental properties. This gives rise to infinitely many toric varieties with a special property, such as being set theoretic complete intersection or arithmetically Cohen-Macaulay (Gorenstein) and having a Cohen-Macaulay tangent cone or a local ring with non-decreasing Hilbert function, from just one singl...