The (pre)triangulated structure on the opposite category #
In this file, we shall construct the (pre)triangulated structure
on the opposite category Cᵒᵖ
of a (pre)triangulated category C
.
The shift on Cᵒᵖ
is obtained by combining the constructions in the files
CategoryTheory.Shift.Opposite
and CategoryTheory.Shift.Pullback
.
When the user opens CategoryTheory.Pretriangulated.Opposite
, the
category Cᵒᵖ
is equipped with the shift by ℤ
such that
shifting by n : ℤ
on Cᵒᵖ
corresponds to the shift by
-n
on C
. This is actually a definitional equality, but the user
should not rely on this, and instead use the isomorphism
shiftFunctorOpIso C n m hnm : shiftFunctor Cᵒᵖ n ≅ (shiftFunctor C m).op
where hnm : n + m = 0
.
Some compatibilities between the shifts on C
and Cᵒᵖ
are also expressed through
the equivalence of categories opShiftFunctorEquivalence C n : Cᵒᵖ ≌ Cᵒᵖ
whose
functor is shiftFunctor Cᵒᵖ n
and whose inverse functor is (shiftFunctor C n).op
.
If X ⟶ Y ⟶ Z ⟶ X⟦1⟧
is a distinguished triangle in C
, then the triangle
op Z ⟶ op Y ⟶ op X ⟶ (op Z)⟦1⟧
that is deduced without introducing signs
shall be a distinguished triangle in Cᵒᵖ
. This is equivalent to the definition
in [Verdiers's thesis, p. 96][verdier1996] which would require that the triangle
(op X)⟦-1⟧ ⟶ op Z ⟶ op Y ⟶ op X
(without signs) is antidistinguished.
References #
- [Jean-Louis Verdier, Des catégories dérivées des catégories abéliennes][verdier1996]
The category Cᵒᵖ
is equipped with the shift such that the shift by n
on Cᵒᵖ
corresponds to the shift by -n
on C
.
Equations
- CategoryTheory.Pretriangulated.Opposite.instHasShiftOppositeInt C = inferInstance
Instances For
Equations
- ⋯ = ⋯
The shift functor on the opposite category identifies to the opposite functor of a shift functor on the original category.
Equations
Instances For
The autoequivalence Cᵒᵖ ≌ Cᵒᵖ
whose functor is shiftFunctor Cᵒᵖ n
and whose inverse
functor is (shiftFunctor C n).op
. Do not unfold the definitions of the unit and counit
isomorphisms: the compatibilities they satisfy are stated as separate lemmas.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The naturality of the unit and counit isomorphisms are restated in the following
lemmas so as to mitigate the need for erw
.
The functor which sends a triangle X ⟶ Y ⟶ Z ⟶ X⟦1⟧
in C
to the triangle
op Z ⟶ op Y ⟶ op X ⟶ (op Z)⟦1⟧
in Cᵒᵖ
(without introducing signs).
Equations
- One or more equations did not get rendered due to their size.
Instances For
The functor which sends a triangle X ⟶ Y ⟶ Z ⟶ X⟦1⟧
in Cᵒᵖ
to the triangle
Z.unop ⟶ Y.unop ⟶ X.unop ⟶ Z.unop⟦1⟧
in C
(without introducing signs).
Equations
- One or more equations did not get rendered due to their size.
Instances For
The unit isomorphism of the
equivalence triangleOpEquivalence C : (Triangle C)ᵒᵖ ≌ Triangle Cᵒᵖ
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The counit isomorphism of the
equivalence triangleOpEquivalence C : (Triangle C)ᵒᵖ ≌ Triangle Cᵒᵖ
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
An anti-equivalence between the categories of triangles in C
and in Cᵒᵖ
.
A triangle in Cᵒᵖ
shall be distinguished iff it correspond to a distinguished
triangle in C
via this equivalence.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A triangle in Cᵒᵖ
shall be distinguished iff it corresponds to a distinguished
triangle in C
via the equivalence triangleOpEquivalence C : (Triangle C)ᵒᵖ ≌ Triangle Cᵒᵖ
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Up to rotation, the contractible triangle X ⟶ X ⟶ 0 ⟶ X⟦1⟧
for X : Cᵒᵖ
corresponds
to the contractible triangle for X.unop
in C
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Isomorphism expressing a compatibility of the equivalence triangleOpEquivalence C
with the rotation of triangles.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The pretriangulated structure on the opposite category of
a pretriangulated category. It is a scoped instance, so that we need to
open CategoryTheory.Pretriangulated.Opposite
in order to be able
to use it: the reason is that it relies on the definition of the shift
on the opposite category Cᵒᵖ
, for which it is unclear whether it should
be a global instance or not.
Equations
- One or more equations did not get rendered due to their size.