Theorem: CategoryTheory.isVanKampenColimit_of_isEmpty
File: Mathlib/CategoryTheory/Limits/VanKampen.lean

Proof steps:
state_before: J : Type v'
inst✝⁵ : Category.{u', v'} J
C : Type u
inst✝⁴ : Category.{v, u} C
K : Type u_1
inst✝³ : Category.{?u.260730, u_1} K
D : Type u_2
inst✝² : Category.{?u.260737, u_2} D
inst✝¹ : HasStrictInitialObjects C
inst✝ : IsEmpty J
F : J ⥤ C
c : Cocone F
hc : IsColimit c
⊢ IsVanKampenColimit c
state_after: J : Type v'
inst✝⁵ : Category.{u', v'} J
C : Type u
inst✝⁴ : Category.{v, u} C
K : Type u_1
inst✝³ : Category.{?u.260730, u_1} K
D : Type u_2
inst✝² : Category.{?u.260737, u_2} D
inst✝¹ : HasStrictInitialObjects C
inst✝ : IsEmpty J
F : J ⥤ C
c : Cocone F
hc : IsColimit c
this : IsInitial c.pt
⊢ IsVanKampenColimit c
tactic: have : IsInitial c.pt := by
    have := (IsColimit.precomposeInvEquiv (Functor.uniqueFromEmpty _) _).symm
      (hc.whiskerEquivalence (equivalenceOfIsEmpty (Discrete PEmpty.{1}) J))
    exact IsColimit.ofIsoColimit this (Cocones.ext (Iso.refl c.pt) (fun {X} ↦ isEmptyElim X))
state_before: J : Type v'
inst✝⁵ : Category.{u', v'} J
C : Type u
inst✝⁴ : Category.{v, u} C
K : Type u_1
inst✝³ : Category.{?u.260730, u_1} K
D : Type u_2
inst✝² : Category.{?u.260737, u_2} D
inst✝¹ : HasStrictInitialObjects C
inst✝ : IsEmpty J
F : J ⥤ C
c : Cocone F
hc : IsColimit c
this : IsInitial c.pt
⊢ IsVanKampenColimit c
state_after: J : Type v'
inst✝⁵ : Category.{u', v'} J
C : Type u
inst✝⁴ : Category.{v, u} C
K : Type u_1
inst✝³ : Category.{?u.260730, u_1} K
D : Type u_2
inst✝² : Category.{?u.260737, u_2} D
inst✝¹ : HasStrictInitialObjects C
inst✝ : IsEmpty J
F : J ⥤ C
c : Cocone F
hc : IsColimit c
this : IsVanKampenColimit (asEmptyCocone c.pt)
⊢ IsVanKampenColimit c
tactic: replace this := IsInitial.isVanKampenColimit this
state_before: J : Type v'
inst✝⁵ : Category.{u', v'} J
C : Type u
inst✝⁴ : Category.{v, u} C
K : Type u_1
inst✝³ : Category.{?u.260730, u_1} K
D : Type u_2
inst✝² : Category.{?u.260737, u_2} D
inst✝¹ : HasStrictInitialObjects C
inst✝ : IsEmpty J
F : J ⥤ C
c : Cocone F
hc : IsColimit c
this : IsVanKampenColimit (asEmptyCocone c.pt)
⊢ IsVanKampenColimit c
state_after: J : Type v'
inst✝⁵ : Category.{u', v'} J
C : Type u
inst✝⁴ : Category.{v, u} C
K : Type u_1
inst✝³ : Category.{?u.260730, u_1} K
D : Type u_2
inst✝² : Category.{?u.260737, u_2} D
inst✝¹ : HasStrictInitialObjects C
inst✝ : IsEmpty J
F : J ⥤ C
c : Cocone F
hc : IsColimit c
this : IsVanKampenColimit (asEmptyCocone c.pt)
⊢ IsVanKampenColimit (Cocone.whisker (equivalenceOfIsEmpty (Discrete PEmpty.{1}) J).functor c)
tactic: apply (IsVanKampenColimit.whiskerEquivalence_iff
    (equivalenceOfIsEmpty (Discrete PEmpty.{1}) J)).mp
state_before: J : Type v'
inst✝⁵ : Category.{u', v'} J
C : Type u
inst✝⁴ : Category.{v, u} C
K : Type u_1
inst✝³ : Category.{?u.260730, u_1} K
D : Type u_2
inst✝² : Category.{?u.260737, u_2} D
inst✝¹ : HasStrictInitialObjects C
inst✝ : IsEmpty J
F : J ⥤ C
c : Cocone F
hc : IsColimit c
this : IsVanKampenColimit (asEmptyCocone c.pt)
⊢ IsVanKampenColimit (Cocone.whisker (equivalenceOfIsEmpty (Discrete PEmpty.{1}) J).functor c)
state_after: no goals
tactic: exact (this.precompose_isIso (Functor.uniqueFromEmpty
    ((equivalenceOfIsEmpty (Discrete PEmpty.{1}) J).functor ⋙ F)).hom).of_iso
    (Cocones.ext (Iso.refl _) (by simp))