弱群余代数的交叉积

该文引入弱群交叉积的概念,并给出弱群交叉积代数和通常的张量积余代数构成弱半Hopf群余代数的充要条件,接着证明了弱群交叉积上的对偶定理,推广了沈和王^([7-8])的主要结果.

弱广义对角交叉积的表示范畴

引入弱(H,A)-Yetter Drinfeld模和弱广义对角交叉积代数,证明了弱广义对角交叉积的表示范畴同构于弱(H,A)-Yetter Drinfeld模范畴.

弱Hopf Galois扩张的Cotorsion维数

考虑在Ext群上构造Grothendieck谱序列揭示弱Hopf Galois扩张的cotorsion维数.设H为有限维弱Hopf代数,A/B为弱H-Galois扩张,给出A,B的左cotorsion维数与H的右整体维数之间的关系,并讨论当B为可换的或H*为半单时,A,B的左cotorsion维数的性质.

弱斜配对双代数和弱相关Long双代数

该文在弱双代数H上给出了扭曲积(H~σ,·σ)成为弱双代数的充分必要条件．设[B,H,τ]是一个弱斜配对,并且τ可逆,则在某个条件下弱双交叉积B _τH是一个弱双代数．如果(B,H,σ)是弱相关Long双代数,并且σ可逆,则弱双交叉积B^(OP) _σH可以被构造．它的乘法是：(x h)(y g)=∑σ(y_1,h_1)y_2 x h_2gσ^(-1)(y_3,h_3),特别地,如果(B,H,σ)是相关Long双代数,则(B^(OP) _σH,β)是Long双代数当且仅当对任意b,d∈B^(OP)；g,∈H,∑_σ^(-1) (b,g_2 )σ(d,g_1)=∑σ^(-1)(b, g_1)σ(d,g_2),其中B为H的子Hopf代数,β定义为β(b _σh c _σg)=ε_H(h)ε_B^(OP)(c)σ^(-1)(b,g)．对于Sweedler 4维Hopf代数H,作者给出一个例子说明：此弱双交叉积(B^(OP) _σH,β)不仅是一个Long双代数,而且是一个非可换和非余可换的8维Hopf代数．最后,设B,H都是弱双代数,σ：B H→k是一个线性映射,作者给出了(B,σ,,Δ_B)是弱相关右(H,B)-重模代数的充分必要条件．

Crossed Products over Weak Hopf Algebras Related to Cleft Extensions and Cohomology

The authors present the general theory of cleft extensions for a cocommutative weak Hopf algebra H. For a right H-comodule algebra, they obtain a bijective corre- spondence between the isomorphisms classes of H-cleft extensions AH → A, where AH is the subalgebra of coinvariants, and the equivalence classes of crossed systems for H over AH. Finally, they establish a bijection between the set of equivalence classes of crossed systems with a fixed weak H-module algebra structure and the second cohomology group H2φZ（AH） （H, Z（AH））, where Z（AH） is the center of AH.