We investigate the behavior of the test ideal of an excellent reduced ring of prime characteristic under base change. It is shown that if h : A ?! D is a smooth homomorphism, then A D = D , assuming that all residue elds of A at maximal ideals are perfect and that formation of the test ideal commutes with localization. It is also shown that if h : (A; m) ?! D is a nite at homomorphism of Gorens...

These are notes of two talks with the aim of giving some basic properties of the endomorphism ring of an Abelian variety A and its representations on certain linear objects associated to A. The results can be found in § 5.1 of Shimura’s book [1], but presented in a completely different way. For completeness, we state some definitions. An Abelian variety over a field k is a proper, smooth, conne...

We show that certain canonical realizations of the complexes Hom(G,H) and Hom+(G,H) of (partial) graph homomorphisms studied by Babson and Kozlov are in fact instances of the polyhedral Cayley trick. For G a complete graph, we then characterize when a canonical projection of these complexes is itself again a complex, and exhibit several well-known objects that arise as cells or subcomplexes of ...

...

Let Gn,k denote the Kneser graph whose vertices are the n-element subsets of a (2n + k)-element set and whose edges are the disjoint pairs. In this paper we prove that for any non-negative integer s there is no graph homomorphism from G4,2 to G4s+1,2s+1. This confirms a conjecture of Stahl in a special case.

A multiplication on an Abelian group G is a homomorphism μ: ⊗ → G. An with it called ring the R. A. Beaumont and D. Lawver have formulated problem of studying semisimple groups. said to be if there exists associative it. Semisimple groups are described in class vector nonmeasurable It also shown that set I nonmeasurable, $$ G=\coprod_{i\in I}{A}_i reduced group, μ G, then determined by its rest...

In this article, we study the structure of finitely ramified mixed characteristic valued fields. For any two complete discrete fields K 1 and 2 with perfect residue fields, show that if n -th rings are isomorphic for each ? , then isometric isomorphic. More generally, there is depending only on ramification indices such homomorphism from ring to can be lifted a between valuation rings. Moreover...

We investigate the algebra of a Hausdorff ample groupoid, introduced by Steinberg, over commutative semiring S. In particular, we obtain complete characterization congruence-simpleness for such Steinberg algebras, extending well-known characterizations when S is field or ring. also provide criterion AS(GE) graph groupoid GE associated to an arbitrary E be congruence-simple. Motivated result Cla...

We show that any pointed, peordered module map BFgr(E)→BFgr(F) between Bowen-Franks modules of finite graphs can be lifted to a unital, graded, diagonal preserving ⁎-homomorphism Lℓ(E)→Lℓ(F) the corresponding Leavitt path algebras over commutative unital ring with involution ℓ. Specializing case when ℓ is field, we establish fullness part Hazrat's conjecture about functor from ℓ-algebras preord...