-- Mathlib/CategoryTheory/Limits/Shapes/Products.lean
theorem Sigma.ι_reindex_hom (b : β) :
    Sigma.ι (f ∘ ε) b ≫ (Sigma.reindex ε f).hom = Sigma.ι f (ε b)

Proof state:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
⊢ ι (f ∘ ⇑ε) b ≫ (reindex ε f).hom = ι f (ε b)

Tactic:
dsimp [Sigma.reindex]

Result:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
⊢ ι (f ∘ ⇑ε) b ≫
      (HasColimit.isoOfEquivalence (Discrete.equivalence ε) (Discrete.natIso fun x => Iso.refl (f (ε x.as)))).hom =
    ι f (ε b)

Proof state:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
h :
  (Discrete.functor f).map (Discrete.eqToHom' ⋯) ≫ colimit.ι (Discrete.functor f) { as := ε b } =
    colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) }
⊢ (Discrete.functor (f ∘ ⇑ε)).map ((Discrete.equivalence ε).unit.app { as := b }) ≫
      colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) } =
    ι f (ε b)

Tactic:
erw [← h, eqToHom_map, eqToHom_map, eqToHom_trans_assoc]

Result:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
h :
  (Discrete.functor f).map (Discrete.eqToHom' ⋯) ≫ colimit.ι (Discrete.functor f) { as := ε b } =
    colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) }
⊢ eqToHom ⋯ ≫ colimit.ι (Discrete.functor f) { as := ε b } = ι f (ε b)

case p
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
h :
  (Discrete.functor f).map (Discrete.eqToHom' ⋯) ≫ colimit.ι (Discrete.functor f) { as := ε b } =
    colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) }
⊢ { as := b } = { as := ε.symm (ε b) }

Proof state:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
⊢ ι (f ∘ ⇑ε) b ≫
      (HasColimit.isoOfEquivalence (Discrete.equivalence ε) (Discrete.natIso fun x => Iso.refl (f (ε x.as)))).hom =
    ι f (ε b)

Tactic:
simp only [HasColimit.isoOfEquivalence_hom_π, Functor.id_obj, Discrete.functor_obj,
  Function.comp_apply, Discrete.equivalence_functor, Discrete.equivalence_inverse,
  Functor.comp_obj, Discrete.natIso_inv_app, Iso.refl_inv, Category.id_comp]

Result:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
⊢ (Discrete.functor (f ∘ ⇑ε)).map ((Discrete.equivalence ε).unit.app { as := b }) ≫
      colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) } =
    ι f (ε b)

Proof state:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
h :
  (Discrete.functor f).map (Discrete.eqToHom' ⋯) ≫ colimit.ι (Discrete.functor f) { as := ε b } =
    colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) }
⊢ eqToHom ⋯ ≫ colimit.ι (Discrete.functor f) { as := ε b } = ι f (ε b)

case p
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
h :
  (Discrete.functor f).map (Discrete.eqToHom' ⋯) ≫ colimit.ι (Discrete.functor f) { as := ε b } =
    colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) }
⊢ { as := b } = { as := ε.symm (ε b) }

Tactic:
all_goals { simp }

Result:
no goals

Proof state:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
⊢ (Discrete.functor (f ∘ ⇑ε)).map ((Discrete.equivalence ε).unit.app { as := b }) ≫
      colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) } =
    ι f (ε b)

Tactic:
have h := colimit.w (Discrete.functor f) (Discrete.eqToHom' (ε.apply_symm_apply (ε b)))

Result:
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
h :
  (Discrete.functor f).map (Discrete.eqToHom' ⋯) ≫ colimit.ι (Discrete.functor f) { as := ε b } =
    colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) }
⊢ (Discrete.functor (f ∘ ⇑ε)).map ((Discrete.equivalence ε).unit.app { as := b }) ≫
      colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) } =
    ι f (ε b)

Proof state:
case p
β : Type w
C : Type u
inst✝² : Category.{v, u} C
γ : Type w'
ε : β ≃ γ
f : γ → C
inst✝¹ : HasCoproduct f
inst✝ : HasCoproduct (f ∘ ⇑ε)
b : β
h :
  (Discrete.functor f).map (Discrete.eqToHom' ⋯) ≫ colimit.ι (Discrete.functor f) { as := ε b } =
    colimit.ι (Discrete.functor f) { as := ε (ε.symm (ε b)) }
⊢ { as := b } = { as := ε.symm (ε b) }

Tactic:
simp

Result:
no goals