A cohomological δ-functor (Definition 43, Lecture 22–23): a sequence of additive functors
T n : C ⥤ D together with connecting morphisms δ and the long-exact-sequence and
naturality data attached to each short exact sequence in C.
- T : ℕ → CategoryTheory.Functor C D
- leftExact : CategoryTheory.Limits.PreservesFiniteLimits (self.T 0)
- comp_δ_zero (n : ℕ) (S : CategoryTheory.ShortComplex C) (hS : S.ShortExact) : CategoryTheory.CategoryStruct.comp ((self.T n).map S.g) (self.δ n S hS) = 0
- δ_comp_zero (n : ℕ) (S : CategoryTheory.ShortComplex C) (hS : S.ShortExact) : CategoryTheory.CategoryStruct.comp (self.δ n S hS) ((self.T (n + 1)).map S.f) = 0
- δ_natural (n : ℕ) (S S' : CategoryTheory.ShortComplex C) (hS : S.ShortExact) (hS' : S'.ShortExact) (φ : S ⟶ S') : CategoryTheory.CategoryStruct.comp ((self.T n).map φ.τ₃) (self.δ n S' hS') = CategoryTheory.CategoryStruct.comp (self.δ n S hS) ((self.T (n + 1)).map φ.τ₁)
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A morphism of cohomological δ-functors F ⟶ G is a sequence of natural transformations
η n : F.T n ⟶ G.T n compatible with the connecting maps δ of F and G.
- comm_δ (n : ℕ) (S : CategoryTheory.ShortComplex C) (hS : S.ShortExact) : CategoryTheory.CategoryStruct.comp ((self.η n).app S.X₃) (G.δ n S hS) = CategoryTheory.CategoryStruct.comp (F.δ n S hS) ((self.η (n + 1)).app S.X₁)
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The universal property defining a derived functor (Definition 44–45, Lecture 22–23):
a δ-functor F is universal if every degree-zero natural transformation F.T 0 ⟶ G.T 0
extends uniquely to a morphism of δ-functors.
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The n-th right derived functor of an additive functor F : C ⥤ D.
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The induced natural transformation between n-th right derived functors from a natural
transformation F ⟶ G.
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For a left-exact additive functor, the zeroth right derived functor is naturally isomorphic to the functor itself.
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Right derived functors in positive degree vanish on injective objects.
The canonical natural transformation from F to its zeroth right derived functor.