Categorical Aspects in Projective Geometry

After introducing morphisms between projective geometries, some categorical questions are examined. It is shown that there are three kinds of embeddings and two kinds of quotients. Furthermore the morphisms decompose in a canonical way into four factors.     

范畴中态射集星型序的刻划

本文证得了带有对合＊范畴中态射集的左（右）星序的１２种刻划，得到了此范畴中态射集的星序的２０种刻划，将［１－５］中复矩阵的相应结果推广范畴中。     

关于态射的广义Moore-Penrose逆

本文研究了态射的广义Moore-Penrose逆．给出了范畴中态射的广义Moore-Penrose逆存在的一些新的充要条件．也给出了广义Moore-Penrose逆的乘积公式成立的充要条件。     

加法范畴中态射的Drazin逆

本文研究了加法范畴上态射的Drazin逆。首先给出了态射和φ η与态射φ有Drazin逆的一个关系，得到了φ η的Drazin逆的一个公式，其次证明了态射φ有Drazin逆当且仅当φ^k有群逆（k为某一正整数）。最后还证明了：如果2为可逆态射，则具有Drazin逆的态射一定为两个可逆态射之和。     

Noncommutative schemes

The main purpose of this work is to introduce noncommutative relative schemes and establish some of basic properties of schemes and scheme morphisms. In particular, we prove an analogue of the canonical bijection: ((X, O), Spec(A)) Hom (A, (X, O)). We define a noncommutative version of the ech cohomology of an affine cover and show that the ech cohomology can be used to compute higher direct images. This fact is applied here to compute cohomology of invertible sheaves on skew projective spaces and in [LR3] to study D-modules on quantum flag varieties.     

Projective push-forwards in the Witt theory of algebraic varieties

We define push-forwards along projective morphisms in the Witt theory of smooth quasi-projective varieties over a field. We prove that they have standard properties such as functoriality, compatibility with pull-backs and projection formulas.     

Finite morphisms of projective and K■hler manifolds

In this paper we study finite morphisms of projective and compact K■hler manifolds, in particular,positivity properties of the associated vector bundle,deformation theory and ramified endomorphisms.     

Iterated inverse images of plane curve singularities

We describe the evolution of certain multiplicities and intersection numbers of plane curve singularities under the iterated action of an analytic morphism.     

Preservation of quasi-isomorphisms of complexes

We consider the preservation property of the homomorphism and tensor product functors for quasi-isomorphisms and equivalences of complexes.Let X and Y be two classes of R-modules with Ext ≥1(X,Y) = 0 for each object X ∈X and each object Y ∈Y.We show that if A,B ∈C■(R) are X-complexes and U,V ∈ C■(R) are Y-complexes,then U■V■Hom(A,U)■Hom(A,V);A■B■Hom(B,U)■Hom(A,U).As an application,we give a sufficient condition for the Hom evaluation morphism being invertible.