| Let G be a group with unit e,A a ring with unit,and(?)a G-group A-coring,(or shortly a G-A-coring).In[1],the definition of G-A-coring were introduced,and some new properties about G-A-coring were studied.A systematic algebraic studuy of structures about A-corings has been carried out in[2].This paper wants to show some other good results,we state the main results as follows.In section 3,Similarly as for comodules of A-corings[1],it will turn out that,comodules of G-A-corings are closely related to modules over the dual rings.In the case of G-Acorings there are dule rings~*(?)and(?)~*,and the right(?)-comodules are left modules of the former while the left comodules are right modules of the latter.In section 4,we define the coideal of G-A-corings,and we recall the definition of a grouplike element g[1],collect their basic proteries,introduce the corresponding gcoinvariants funtor and view it as a Hom-funtor,study the Hom-tensor relations about G-A-corings.In section 5,the cotensor product for comodules over corings is extended to the cotensor product of comodules over G-A-corings.The corresponding properties relations, coflatness,purity,and so on,are studied. |
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