-- Mathlib/CategoryTheory/Limits/Constructions/LimitsOfProductsAndEqualizers.lean
/-- If a functor preserves coequalizers and the appropriate coproducts, it preserves colimits. -/
lemma preservesColimit_of_preservesCoequalizers_and_coproduct :
    PreservesColimitsOfShape J G where
  preservesColimit {K}

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
J : Type w
inst✝⁷ : SmallCategory J
D : Type u₂
inst✝⁶ : Category.{v₂, u₂} D
inst✝⁵ : HasColimitsOfShape (Discrete J) C
inst✝⁴ : HasColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) C
inst✝³ : HasCoequalizers C
G : C ⥤ D
inst✝² : PreservesColimitsOfShape WalkingParallelPair G
inst✝¹ : PreservesColimitsOfShape (Discrete J) G
inst✝ : PreservesColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) G
K : J ⥤ C
P : C := ∐ K.obj
Q : C := ∐ fun f => K.obj f.fst.1
s : Q ⟶ P := Sigma.desc fun f => K.map f.snd ≫ colimit.ι (Discrete.functor K.obj) { as := f.fst.2 }
t : Q ⟶ P := Sigma.desc fun f => colimit.ι (Discrete.functor K.obj) { as := f.fst.1 }
I : C := coequalizer s t
⊢ PreservesColimit K G

Tactic:
let i : P ⟶ I := coequalizer.π s t

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
J : Type w
inst✝⁷ : SmallCategory J
D : Type u₂
inst✝⁶ : Category.{v₂, u₂} D
inst✝⁵ : HasColimitsOfShape (Discrete J) C
inst✝⁴ : HasColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) C
inst✝³ : HasCoequalizers C
G : C ⥤ D
inst✝² : PreservesColimitsOfShape WalkingParallelPair G
inst✝¹ : PreservesColimitsOfShape (Discrete J) G
inst✝ : PreservesColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) G
K : J ⥤ C
P : C := ∐ K.obj
Q : C := ∐ fun f => K.obj f.fst.1
s : Q ⟶ P := Sigma.desc fun f => K.map f.snd ≫ colimit.ι (Discrete.functor K.obj) { as := f.fst.2 }
t : Q ⟶ P := Sigma.desc fun f => colimit.ι (Discrete.functor K.obj) { as := f.fst.1 }
I : C := coequalizer s t
i : P ⟶ I := coequalizer.π s t
⊢ PreservesColimit K G

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
J : Type w
inst✝⁷ : SmallCategory J
D : Type u₂
inst✝⁶ : Category.{v₂, u₂} D
inst✝⁵ : HasColimitsOfShape (Discrete J) C
inst✝⁴ : HasColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) C
inst✝³ : HasCoequalizers C
G : C ⥤ D
inst✝² : PreservesColimitsOfShape WalkingParallelPair G
inst✝¹ : PreservesColimitsOfShape (Discrete J) G
inst✝ : PreservesColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) G
K : J ⥤ C
P : C := ∐ K.obj
Q : C := ∐ fun f => K.obj f.fst.1
s : Q ⟶ P := Sigma.desc fun f => K.map f.snd ≫ colimit.ι (Discrete.functor K.obj) { as := f.fst.2 }
t : Q ⟶ P := Sigma.desc fun f => colimit.ι (Discrete.functor K.obj) { as := f.fst.1 }
I : C := coequalizer s t
i : P ⟶ I := coequalizer.π s t
⊢ PreservesColimit K G

Tactic:
apply preservesColimit_of_preserves_colimit_cocone
    (buildIsColimit s t (by simp [P, s]) (by simp [P, t]) (colimit.isColimit _)
      (colimit.isColimit _) (colimit.isColimit _))

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
J : Type w
inst✝⁷ : SmallCategory J
D : Type u₂
inst✝⁶ : Category.{v₂, u₂} D
inst✝⁵ : HasColimitsOfShape (Discrete J) C
inst✝⁴ : HasColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) C
inst✝³ : HasCoequalizers C
G : C ⥤ D
inst✝² : PreservesColimitsOfShape WalkingParallelPair G
inst✝¹ : PreservesColimitsOfShape (Discrete J) G
inst✝ : PreservesColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) G
K : J ⥤ C
P : C := ∐ K.obj
Q : C := ∐ fun f => K.obj f.fst.1
s : Q ⟶ P := Sigma.desc fun f => K.map f.snd ≫ colimit.ι (Discrete.functor K.obj) { as := f.fst.2 }
t : Q ⟶ P := Sigma.desc fun f => colimit.ι (Discrete.functor K.obj) { as := f.fst.1 }
I : C := coequalizer s t
i : P ⟶ I := coequalizer.π s t
⊢ IsColimit (G.mapCocone (buildColimit s t ⋯ ⋯ (colimit.cocone (parallelPair s t))))

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
J : Type w
inst✝⁷ : SmallCategory J
D : Type u₂
inst✝⁶ : Category.{v₂, u₂} D
inst✝⁵ : HasColimitsOfShape (Discrete J) C
inst✝⁴ : HasColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) C
inst✝³ : HasCoequalizers C
G : C ⥤ D
inst✝² : PreservesColimitsOfShape WalkingParallelPair G
inst✝¹ : PreservesColimitsOfShape (Discrete J) G
inst✝ : PreservesColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) G
K : J ⥤ C
P : C := ∐ K.obj
Q : C := ∐ fun f => K.obj f.fst.1
s : Q ⟶ P := Sigma.desc fun f => K.map f.snd ≫ colimit.ι (Discrete.functor K.obj) { as := f.fst.2 }
t : Q ⟶ P := Sigma.desc fun f => colimit.ι (Discrete.functor K.obj) { as := f.fst.1 }
I : C := coequalizer s t
i : P ⟶ I := coequalizer.π s t
⊢ ∀ (j : J),
    (buildColimit (G.map s) (G.map t) ⋯ ⋯ (Cofork.ofπ (G.map i) ⋯)).ι.app j ≫
        (Iso.refl (buildColimit (G.map s) (G.map t) ⋯ ⋯ (Cofork.ofπ (G.map i) ⋯)).pt).hom =
      (G.mapCocone (buildColimit s t ⋯ ⋯ (colimit.cocone (parallelPair s t)))).ι.app j

Tactic:
intro j

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
J : Type w
inst✝⁷ : SmallCategory J
D : Type u₂
inst✝⁶ : Category.{v₂, u₂} D
inst✝⁵ : HasColimitsOfShape (Discrete J) C
inst✝⁴ : HasColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) C
inst✝³ : HasCoequalizers C
G : C ⥤ D
inst✝² : PreservesColimitsOfShape WalkingParallelPair G
inst✝¹ : PreservesColimitsOfShape (Discrete J) G
inst✝ : PreservesColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) G
K : J ⥤ C
P : C := ∐ K.obj
Q : C := ∐ fun f => K.obj f.fst.1
s : Q ⟶ P := Sigma.desc fun f => K.map f.snd ≫ colimit.ι (Discrete.functor K.obj) { as := f.fst.2 }
t : Q ⟶ P := Sigma.desc fun f => colimit.ι (Discrete.functor K.obj) { as := f.fst.1 }
I : C := coequalizer s t
i : P ⟶ I := coequalizer.π s t
j : J
⊢ (buildColimit (G.map s) (G.map t) ⋯ ⋯ (Cofork.ofπ (G.map i) ⋯)).ι.app j ≫
      (Iso.refl (buildColimit (G.map s) (G.map t) ⋯ ⋯ (Cofork.ofπ (G.map i) ⋯)).pt).hom =
    (G.mapCocone (buildColimit s t ⋯ ⋯ (colimit.cocone (parallelPair s t)))).ι.app j

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
J : Type w
inst✝⁷ : SmallCategory J
D : Type u₂
inst✝⁶ : Category.{v₂, u₂} D
inst✝⁵ : HasColimitsOfShape (Discrete J) C
inst✝⁴ : HasColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) C
inst✝³ : HasCoequalizers C
G : C ⥤ D
inst✝² : PreservesColimitsOfShape WalkingParallelPair G
inst✝¹ : PreservesColimitsOfShape (Discrete J) G
inst✝ : PreservesColimitsOfShape (Discrete ((p : J × J) × (p.1 ⟶ p.2))) G
K : J ⥤ C
P : C := ∐ K.obj
Q : C := ∐ fun f => K.obj f.fst.1
s : Q ⟶ P := Sigma.desc fun f => K.map f.snd ≫ colimit.ι (Discrete.functor K.obj) { as := f.fst.2 }
t : Q ⟶ P := Sigma.desc fun f => colimit.ι (Discrete.functor K.obj) { as := f.fst.1 }
I : C := coequalizer s t
i : P ⟶ I := coequalizer.π s t
f : (p : J × J) × (p.1 ⟶ p.2)
⊢ G.map
      ((Cofan.mk (∐ K.obj) fun f => K.map f.snd ≫ colimit.ι (Discrete.functor K.obj) { as := f.fst.2 }).ι.app
        { as := f }) =
    G.map (K.map f.snd ≫ Sigma.ι K.obj f.fst.2)

Tactic:
congr

Result:
no goals