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Mathlib.CategoryTheory.Triangulated.Opposite.Functor

Opposites of functors between pretriangulated categories, #

If F : C ⥤ D is a functor between pretriangulated categories, we prove that F is a triangulated functor if and only if F.op is a triangulated functor. In order to do this, we first show that a CommShift structure on F naturally gives one on F.op (for the shifts on Cᵒᵖ and Dᵒᵖ defined in CategoryTheory.Triangulated.Opposite.Basic), and we then prove that F.mapTriangle.op and F.op.mapTriangle correspond to each other via the equivalences (Triangle C)ᵒᵖ ≌ Triangle Cᵒᵖ and (Triangle D)ᵒᵖ ≌ Triangle Dᵒᵖ given by CategoryTheory.Pretriangulated.triangleOpEquivalence.

If F commutes with shifts, so does F.op, for the shifts chosen on Cᵒᵖ in CategoryTheory.Triangulated.Opposite.Basic.

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      If F : C ⥤ D commutes with shifts, this expresses the compatibility of F.mapTriangle with the equivalences Pretriangulated.triangleOpEquivalence on C and D.

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          If F : C ⥤ D commutes with shifts, this expresses the compatibility of F.mapTriangle with the equivalences Pretriangulated.triangleOpEquivalence on C and D.

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              If F : C ⥤ D commutes with shifts, this expresses the compatibility of F.mapTriangle with the equivalences Pretriangulated.triangleOpEquivalence on C and D.

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                  F is triangulated if and only if F.op is triangulated.