Corings with decomposition and semiperfect corings

Comodules over semiperfect corings

We discuss when the Rat functor associated to a coring satisfying the left $α$-condition is exact. We study the category of comodules over a semiperfect coring. We characterize semiperfect corings over artinian rings and over qF-rings.

Semisimple corings

While semisimple artinian rings and semisimple coalgebras over a field can be described in terms of matrices (either matrix ring over division rings or comatrix coalgebras over the ground field), semisimple corings seem to have a more intrincated structure in general. It turns out that some well-known properties of semisimple rings or coalgebras, which are immediately deduced from the aforementioned structure, are not evident over a (left) semi-simple coring. For instance, it is not evident that the notion of semi-simple coring is left-right symmetric. To be precise, if every left comodule dec…

单模的自同态环与块分解

Endomorphism rings of simple modules and block decomposition

本文利用左右诺特半完全环不可分解性的特征刻画，通过Ext群研究单模，证明不可分解半完全环的单模基数及自同态环特征的一致性，并在拟Frobenius环情形下强化了结果。

相对大投射模及其在直和分解中的应用

Relatively big projective modules and their applications to direct sum decompositions

本文扩展了可数生成投射模相对于迹理想总是相对大的环的例子列表，证明其包括满足多项式恒等式的右noetherian环及$h$-局部整环上的局部半完备无挠代数，并以此完整刻画了Krull维数为1的$h$-局部整环上有限生成无挠模直和项的分解性质。