Sequences of functors from a category equipped with a shift
Let F : C ⥤ A be a functor from a category C that is equipped with a
shift by an additive monoid M. In this file, we define a typeclass
F.ShiftSequence M which includes the data of a sequence of functors
F.shift a : C ⥤ A for all a : A. For each a : A, we have
an isomorphism F.isoShift a : shiftFunctor C a ⋙ F ≅ F.shift a which
satisfies some coherence relations. This allows to state results
(e.g. the long exact sequence of an homology functor (TODO)) using
functors F.shift a rather than shiftFunctor C a ⋙ F. The reason
for this design is that we can often choose functors F.shift a that
have better definitional properties than shiftFunctor C a ⋙ F.
For example, if C is the derived category (TODO) of an abelian
category A and F is the homology functor in degree 0, then
for any n : ℤ, we may choose F.shift n to be the homology functor
in degree n.
A shift sequence for a functor F : C ⥤ A when C is equipped with a shift
by a monoid M involves a sequence of functor sequence n : C ⥤ A for all n : M
which behave like shiftFunctor C n ⋙ F.
- sequence : M → Functor C A
a sequence of functors
sequence 0identifies to the given functorcompatibility isomorphism with the shift
- shiftIso_zero (a : M) : shiftIso 0 a a ⋯ = isoWhiskerRight (shiftFunctorZero C M) (sequence F a) ≪≫ (sequence F a).leftUnitor
- shiftIso_add (n m a a' a'' : M) (ha' : n + a = a') (ha'' : m + a' = a'') : shiftIso (m + n) a a'' ⋯ = isoWhiskerRight (shiftFunctorAdd C m n) (sequence F a) ≪≫ (shiftFunctor C m).associator (shiftFunctor C n) (sequence F a) ≪≫ isoWhiskerLeft (shiftFunctor C m) (shiftIso n a a' ha') ≪≫ shiftIso m a' a'' ha''
Instances
The tautological shift sequence on a functor.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The shifted functors given by the shift sequence.
Equations
Instances For
Compatibility isomorphism shiftFunctor C n ⋙ F.shift a ≅ F.shift a' when n + a = a'.
Equations
- F.shiftIso n a a' ha' = CategoryTheory.Functor.ShiftSequence.shiftIso n a a' ha'
Instances For
The canonical isomorphism F.shift 0 ≅ F.
Equations
Instances For
The canonical isomorphism shiftFunctor C n ⋙ F ≅ F.shift n.
Equations
- F.isoShift n = CategoryTheory.isoWhiskerLeft (CategoryTheory.shiftFunctor C n) (F.isoShiftZero M).symm ≪≫ F.shiftIso n 0 n ⋯
Instances For
The morphism (F.shift a).obj X ⟶ (F.shift a').obj Y induced by a morphism
f : X ⟶ Y⟦n⟧ when n + a = a'.
Equations
Instances For
When f : X ⟶ Y⟦m⟧, m + n = mn, n + a = a' and ha'' : m + a' = a'', this lemma
relates the two morphisms F.shiftMap f a' a'' ha'' and (F.shift a).map (f⟦n⟧'). Indeed,
via canonical isomorphisms, they both identity to morphisms
(F.shift a').obj X ⟶ (F.shift a'').obj Y.
If f : X ⟶ Y⟦m⟧, n + m = 0 and ha' : m + a = a', this lemma relates the two
morphisms F.shiftMap f a a' ha' and (F.shift a').map (f⟦n⟧'). Indeed,
via canonical isomorphisms, they both identify to morphisms
(F.shift a).obj X ⟶ (F.shift a').obj Y.