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chore(CategoryTheory): fix diamond for the preadditive structure on the opposite category #38281

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chore(CategoryTheory): fix diamond for the preadditive structure on the opposite category #38281

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chore(CategoryTheory): fix diamond for the preadditive structure on t…
joelriou Apr 20, 2026
4271023
fix
joelriou Apr 20, 2026
3d84987
fix
joelriou Apr 20, 2026
7a62c77
added test
joelriou Apr 20, 2026
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4 changes: 2 additions & 2 deletions Mathlib/Algebra/Homology/Opposite.lean
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Expand Up @@ -426,10 +426,10 @@ section

variable [Preadditive V]

set_option backward.isDefEq.respectTransparency false in
example : Preadditive (HomologicalComplex Vᵒᵖ c) := inferInstance

instance opFunctor_additive : (@opFunctor ι V _ c _).Additive where

set_option backward.isDefEq.respectTransparency false in
instance unopFunctor_additive : (@unopFunctor ι V _ c _).Additive where

end
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8 changes: 7 additions & 1 deletion Mathlib/CategoryTheory/Preadditive/Opposite.lean
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Expand Up @@ -25,10 +25,16 @@ namespace CategoryTheory
variable (C : Type*) [Category* C] [Preadditive C]

instance : Preadditive Cᵒᵖ where
homGroup X Y := Equiv.addCommGroup (opEquiv X Y)
homGroup X Y := fast_instance% Equiv.addCommGroup (opEquiv X Y)
add_comp _ _ _ f f' g := Quiver.Hom.unop_inj (Preadditive.comp_add _ _ _ g.unop f.unop f'.unop)
comp_add _ _ _ f g g' := Quiver.Hom.unop_inj (Preadditive.add_comp _ _ _ g.unop g'.unop f.unop)

/-- Test that the two ways to obtain the `HasZeroMorphisms Cᵒᵖ` instance
from `Preadditive C` are the same. -/
example : (instPreadditiveOpposite C).preadditiveHasZeroMorphisms =
@Limits.hasZeroMorphismsOpposite C _ Preadditive.preadditiveHasZeroMorphisms := by
with_reducible_and_instances rfl

instance moduleEndLeft {X Y : C} : Module (End X)ᵐᵒᵖ (X ⟶ Y) where
smul_add _ _ _ := Preadditive.comp_add _ _ _ _ _ _
smul_zero _ := Limits.comp_zero
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