ABSTRACT
In this section C https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315140438/b014dc84-a8d0-4f2c-b263-4a2f353a9ffa/content/eq623.tif"/> will be the abelian category of complexes of left R-modules. For objects C and D of C , https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315140438/b014dc84-a8d0-4f2c-b263-4a2f353a9ffa/content/eq624.tif"/> Hom(C, D) is the abelian group of morphisms from C to D in C https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315140438/b014dc84-a8d0-4f2c-b263-4a2f353a9ffa/content/eq625.tif"/> and Exti (C, D) for i ≥ 0 will denote the groups we get from the right derived functor of Hom.
