Module: Mathlib.CategoryTheory.Sites.Precoverage

Goal state before:
pp: C : Type u
inst✝¹ : Category.{v, u} C
J : Precoverage C
inst✝ : J.IsStableUnderComposition
ι : Type w
S : C
X : ι → C
f : (i : ι) → X i ⟶ S
hf : Presieve.ofArrows X f ∈ J.coverings S
σ : ι → Type w'
Y : (i : ι) → σ i → C
g : (i : ι) → (j : σ i) → Y i j ⟶ X i
hg : ∀ (i : ι), Presieve.ofArrows (Y i) (g i) ∈ J.coverings (X i)
ι' : Type (max u v) := ↑(Presieve.ofArrows X f).uncurry
σ' : ι' → Type (max u v) :=
  fun i ↦ ↑(Presieve.ofArrows (Y (Presieve.ofArrows.idx ⋯)) (g (Presieve.ofArrows.idx ⋯))).uncurry
α : Type (max u v) := ↑(Presieve.ofArrows (fun p ↦ Y p.fst p.snd) fun x ↦ g x.fst x.snd ≫ f x.fst).uncurry
τ' : α → Type (max u v) :=
  fun a ↦ ↑(Presieve.ofArrows (Y (Presieve.ofArrows.idx ⋯).fst) (g (Presieve.ofArrows.idx ⋯).fst)).uncurry
fib : ι' ⊕ α → Type (max u v) := fun i ↦ Sum.elim (fun i ↦ σ' i) (fun i ↦ Unit ⊕ τ' i) i
incl : ι' ⊕ α → ι := fun p ↦ Sum.elim (fun i ↦ Presieve.ofArrows.idx ⋯) (fun i ↦ (Presieve.ofArrows.idx ⋯).fst) p
fibincl : (i : ι' ⊕ α) → fib i → σ (incl i) :=
  fun i j ↦
    match i, j with
    | Sum.inl i, j => Presieve.ofArrows.idx ⋯
    | Sum.inr i, j => Sum.elim (fun x ↦ (Presieve.ofArrows.idx ⋯).snd) (fun i_1 ↦ Presieve.ofArrows.idx ⋯) j
⊢ (Presieve.ofArrows (fun p ↦ Y (incl p.fst) (fibincl p.fst p.snd)) fun p ↦
      g (incl p.fst) (fibincl p.fst p.snd) ≫ f (incl p.fst)) ∈
    J.coverings S

Tactic:
refine IsStableUnderComposition.comp_mem_coverings (f := fun i ↦ f (incl i))
        (g := fun i j ↦ g (incl i) (fibincl i j)) ?_ fun i ↦ ?_

Goal state after:
case refine_1
C : Type u
inst✝¹ : Category.{v, u} C
J : Precoverage C
inst✝ : J.IsStableUnderComposition
ι : Type w
S : C
X : ι → C
f : (i : ι) → X i ⟶ S
hf : Presieve.ofArrows X f ∈ J.coverings S
σ : ι → Type w'
Y : (i : ι) → σ i → C
g : (i : ι) → (j : σ i) → Y i j ⟶ X i
hg : ∀ (i : ι), Presieve.ofArrows (Y i) (g i) ∈ J.coverings (X i)
ι' : Type (max u v) := ↑(Presieve.ofArrows X f).uncurry
σ' : ι' → Type (max u v) :=
  fun i ↦ ↑(Presieve.ofArrows (Y (Presieve.ofArrows.idx ⋯)) (g (Presieve.ofArrows.idx ⋯))).uncurry
α : Type (max u v) := ↑(Presieve.ofArrows (fun p ↦ Y p.fst p.snd) fun x ↦ g x.fst x.snd ≫ f x.fst).uncurry
τ' : α → Type (max u v) :=
  fun a ↦ ↑(Presieve.ofArrows (Y (Presieve.ofArrows.idx ⋯).fst) (g (Presieve.ofArrows.idx ⋯).fst)).uncurry
fib : ι' ⊕ α → Type (max u v) := fun i ↦ Sum.elim (fun i ↦ σ' i) (fun i ↦ Unit ⊕ τ' i) i
incl : ι' ⊕ α → ι := fun p ↦ Sum.elim (fun i ↦ Presieve.ofArrows.idx ⋯) (fun i ↦ (Presieve.ofArrows.idx ⋯).fst) p
fibincl : (i : ι' ⊕ α) → fib i → σ (incl i) :=
  fun i j ↦
    match i, j with
    | Sum.inl i, j => Presieve.ofArrows.idx ⋯
    | Sum.inr i, j => Sum.elim (fun x ↦ (Presieve.ofArrows.idx ⋯).snd) (fun i_1 ↦ Presieve.ofArrows.idx ⋯) j
⊢ (Presieve.ofArrows (fun i ↦ X (incl i)) fun i ↦ f (incl i)) ∈ J.coverings S

case refine_2
C : Type u
inst✝¹ : Category.{v, u} C
J : Precoverage C
inst✝ : J.IsStableUnderComposition
ι : Type w
S : C
X : ι → C
f : (i : ι) → X i ⟶ S
hf : Presieve.ofArrows X f ∈ J.coverings S
σ : ι → Type w'
Y : (i : ι) → σ i → C
g : (i : ι) → (j : σ i) → Y i j ⟶ X i
hg : ∀ (i : ι), Presieve.ofArrows (Y i) (g i) ∈ J.coverings (X i)
ι' : Type (max u v) := ↑(Presieve.ofArrows X f).uncurry
σ' : ι' → Type (max u v) :=
  fun i ↦ ↑(Presieve.ofArrows (Y (Presieve.ofArrows.idx ⋯)) (g (Presieve.ofArrows.idx ⋯))).uncurry
α : Type (max u v) := ↑(Presieve.ofArrows (fun p ↦ Y p.fst p.snd) fun x ↦ g x.fst x.snd ≫ f x.fst).uncurry
τ' : α → Type (max u v) :=
  fun a ↦ ↑(Presieve.ofArrows (Y (Presieve.ofArrows.idx ⋯).fst) (g (Presieve.ofArrows.idx ⋯).fst)).uncurry
fib : ι' ⊕ α → Type (max u v) := fun i ↦ Sum.elim (fun i ↦ σ' i) (fun i ↦ Unit ⊕ τ' i) i
incl : ι' ⊕ α → ι := fun p ↦ Sum.elim (fun i ↦ Presieve.ofArrows.idx ⋯) (fun i ↦ (Presieve.ofArrows.idx ⋯).fst) p
fibincl : (i : ι' ⊕ α) → fib i → σ (incl i) :=
  fun i j ↦
    match i, j with
    | Sum.inl i, j => Presieve.ofArrows.idx ⋯
    | Sum.inr i, j => Sum.elim (fun x ↦ (Presieve.ofArrows.idx ⋯).snd) (fun i_1 ↦ Presieve.ofArrows.idx ⋯) j
i : ι' ⊕ α
⊢ (Presieve.ofArrows (fun j ↦ Y (incl i) (fibincl i j)) fun j ↦ g (incl i) (fibincl i j)) ∈ J.coverings (X (incl i))