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A balanced derived bifunctor
Definition
Assume the Axiom of Dependent Choice. Let be abelian categories, let be additive in each variable, let be supplied projective resolution data on a class in , and let be supplied injective resolution data on a class in . Assume moreover that for each fixed the covariant functor is left exact, and that for each fixed the functor is left exact.
A balanced derived bifunctor relative to on consists of the two candidate one-variable right-derived constructions from A bifunctor can be derived in either variable when the relevant resolution data are supplied together with, for every , a natural isomorphism natural in and . These isomorphisms must satisfy:
- in degree , when the two candidates are identified with by The zero-th right derived functor of a left exact functor recovers the functor on and on , the balance isomorphism becomes the identity of ;
- the isomorphisms are natural in both variables in the sense of Natural transformation and its components.
This is a definition relative to the displayed supplied data and ; it does not impose an unquantified condition involving alternative data. The definition records extra comparison data, while the previous proposition only constructs the two candidates.
Depends on
Used by
Dependency tree · two levels
15 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Charles A. Weibel, An Introduction to Homological Algebra, Chapter 2 `Derived Functors` (standard reference, not scraped)