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Satellites give the first derived functor
Statement
Assume the Axiom of Dependent Choice.
Let and be abelian categories, and let be additive.
If has enough projectives, is right exact, and is any universal homological delta functor equipped with a chosen natural isomorphism , then naturally, for every supplied projective resolution datum on all objects of . In this sense the first left satellite of , defined as the degree-one term of a universal homological delta functor extending , agrees with .
If has enough injectives, is left exact, and is any universal cohomological delta functor equipped with a chosen natural isomorphism , then naturally, for every supplied injective resolution datum on all objects of . This is the corresponding first right satellite agreement.
Facts & Assumptions
Given: A universal delta functor extending and the corresponding derived delta functor.
Derived functors are universal delta functors (Derived functors are universal delta functors).
Two universal delta functors equipped with chosen degree-zero identifications to the same functor are uniquely isomorphic (Universal delta functors extending the same degree-zero functor are uniquely isomorphic).
Universality is the structure that defines the satellite terminology used on this page (Universal delta functor).
The derived delta functors come with canonical degree-zero identifications to (Left derived functors form a homological delta functor, Right derived functors form a cohomological delta functor).
Proof
In the homological case, [L1] makes universal and [L4] identifies its degree-zero term canonically with . The given satellite functor is also a universal extension of by [L3]. Therefore [L2] yields a unique isomorphism of delta functors , and its degree-one component is the asserted natural isomorphism .
The cohomological case is identical with in place of . Its degree-one component gives the natural isomorphism .
Depends on
Used by
Nothing in the library uses this result yet.
Dependency tree · two levels
26 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
- Alexandre Grothendieck, Some aspects of homological algebra (Barr translation) (standard reference, not scraped)
- Charles A. Weibel, An Introduction to Homological Algebra, Chapter 2 `Derived Functors` (standard reference, not scraped)