-- Mathlib/CategoryTheory/Preadditive/Biproducts.lean
/-- If the (product-like) biproduct comparison for `F` and `f` is a monomorphism, then `F`
    preserves the biproduct of `f`. For the converse, see `mapBiproduct`. -/
lemma preservesBiproduct_of_mono_biproductComparison {f : J → C} [HasBiproduct f]
    [HasBiproduct (F.obj ∘ f)] [Mono (biproductComparison F f)] : PreservesBiproduct f F

Proof state:
case h.e'_3
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
this : HasProduct fun b => F.obj (f b)
j : J
⊢ ((F.mapIso (biproduct.isoProduct f)).inv ≫ F.biproductComparison f ≫ (biproduct.isoProduct (F.obj ∘ f)).hom) ≫
      Pi.π (fun b => F.obj (f b)) j =
    F.map (Pi.π f j)

Tactic:
simp [← Function.comp_def, ← Functor.map_comp]

Result:
no goals

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
this : HasProduct fun b => F.obj (f b)
⊢ PreservesBiproduct f F

Tactic:
have that : piComparison F f =
    (F.mapIso (biproduct.isoProduct f)).inv ≫
      biproductComparison F f ≫ (biproduct.isoProduct _).hom := by
  ext j
  convert piComparison_comp_π F f j; simp [← Function.comp_def, ← Functor.map_comp]

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
this : HasProduct fun b => F.obj (f b)
that :
  piComparison F f =
    (F.mapIso (biproduct.isoProduct f)).inv ≫ F.biproductComparison f ≫ (biproduct.isoProduct (F.obj ∘ f)).hom
⊢ PreservesBiproduct f F

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
this✝¹ : HasProduct fun b => F.obj (f b)
that :
  piComparison F f =
    (F.mapIso (biproduct.isoProduct f)).inv ≫ F.biproductComparison f ≫ (biproduct.isoProduct (F.obj ∘ f)).hom
this✝ : IsIso (F.biproductComparison f)
this : IsIso (piComparison F f)
⊢ PreservesBiproduct f F

Tactic:
haveI := PreservesProduct.of_iso_comparison F f

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
this✝² : HasProduct fun b => F.obj (f b)
that :
  piComparison F f =
    (F.mapIso (biproduct.isoProduct f)).inv ≫ F.biproductComparison f ≫ (biproduct.isoProduct (F.obj ∘ f)).hom
this✝¹ : IsIso (F.biproductComparison f)
this✝ : IsIso (piComparison F f)
this : PreservesLimit (Discrete.functor f) F
⊢ PreservesBiproduct f F

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
⊢ HasProduct fun b => F.obj (f b)

Tactic:
change HasProduct (F.obj ∘ f)

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
⊢ HasProduct (F.obj ∘ f)

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
this✝ : HasProduct fun b => F.obj (f b)
that :
  piComparison F f =
    (F.mapIso (biproduct.isoProduct f)).inv ≫ F.biproductComparison f ≫ (biproduct.isoProduct (F.obj ∘ f)).hom
this : IsIso (F.biproductComparison f)
⊢ IsIso (piComparison F f)

Tactic:
rw [that]

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
inst✝⁷ : Preadditive C
D : Type u'
inst✝⁶ : Category.{v', u'} D
inst✝⁵ : Preadditive D
F : C ⥤ D
inst✝⁴ : F.PreservesZeroMorphisms
J : Type
inst✝³ : Fintype J
f : J → C
inst✝² : HasBiproduct f
inst✝¹ : HasBiproduct (F.obj ∘ f)
inst✝ : Mono (F.biproductComparison f)
this✝ : HasProduct fun b => F.obj (f b)
that :
  piComparison F f =
    (F.mapIso (biproduct.isoProduct f)).inv ≫ F.biproductComparison f ≫ (biproduct.isoProduct (F.obj ∘ f)).hom
this : IsIso (F.biproductComparison f)
⊢ IsIso ((F.mapIso (biproduct.isoProduct f)).inv ≫ F.biproductComparison f ≫ (biproduct.isoProduct (F.obj ∘ f)).hom)