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We study the subgroup of formed by those -extensions of by in an Abelian category which are ${\rm Hom}{}(,-)$-exact, and present a Baer-like description of this subgroup in terms of certain right derived functors of ${\rm Hom}{}(-,-)$. We also study adjointness properties of these subgroups and the disk and sphere chain complex functors $ \longrightarrow ()$, given by a collection of natural isomorphisms which generalize the corresponding adjointness properties proven by J. Gillespie for .

生成讲解博客的中文版本

生成AI智能校验的中文版本