Module: Mathlib.AlgebraicTopology.SimplicialSet.AnodyneExtensions.UnionProd

Goal state before:
pp: case inr.right
m✝ : ℕ
k✝ : Fin (m✝ + 1)
n✝ : ℕ
x : (Λ[m✝ + 1, k✝.castSucc].unionProd ∂Δ[n✝]).N
d✝ m : ℕ
k : Fin (m + 1)
n d : ℕ
is it : Fin (d + 1)
s : (Δ[m + 1] ⊗ Δ[n]) _⦋d + 1⦌
hs₁ : s ∈ (Δ[m + 1] ⊗ Δ[n]).nonDegenerate (d + 1)
hs₂ : s ∉ (Λ[m + 1, k.castSucc].unionProd ∂Δ[n]).obj (Opposite.op ⦋d + 1⦌)
hs : IsIndex (Subcomplex.N.mk s hs₁ hs₂) ⋯ is.succ
t : (Δ[m + 1] ⊗ Δ[n]) _⦋d + 1⦌
ht₁ : t ∈ (Δ[m + 1] ⊗ Δ[n]).nonDegenerate (d + 1)
ht₂ : t ∉ (Λ[m + 1, k.castSucc].unionProd ∂Δ[n]).obj (Opposite.op ⦋d + 1⦌)
ht : IsIndex (Subcomplex.N.mk t ht₁ ht₂) ⋯ it.succ
h₂ :
  (pairingCore k n).type₂ { x := Subcomplex.N.mk s hs₁ hs₂, d := d, hd := ⋯, index := is, isIndex := hs } <
    (pairingCore k n).type₁ { x := Subcomplex.N.mk t ht₁ ht₂, d := d, hd := ⋯, index := it, isIndex := ht }
h₁ : ¬Subcomplex.N.mk s hs₁ hs₂ = Subcomplex.N.mk t ht₁ ht₂
hf : Mono (SimplexCategory.δ it.succ)
Ss : Finset (Fin ((Subcomplex.N.mk s hs₁ hs₂).dim + 1)) := finset (Subcomplex.N.mk s hs₁ hs₂) ⋯
St : Finset (Fin ((Subcomplex.N.mk t ht₁ ht₂).dim + 1)) := finset (Subcomplex.N.mk t ht₁ ht₂) ⋯
Sδ : Finset (Fin (hs.δ.dim + 1)) := finset hs.δ ⋯
hδ : ∀ (i : Fin (d + 1)), s.1 (is.castSucc.succAbove i) = t.1 (it.succ.succAbove i)
hSs : ∀ (i : Fin (d + 1)), i ∈ Sδ ↔ is.castSucc.succAbove i ∈ Ss
hSt : ∀ (i : Fin (d + 1)), i ∈ Sδ ↔ it.succ.succAbove i ∈ St
i : Fin ((Subcomplex.N.mk t ht₁ ht₂).dim + 1)
⊢ i ∈ St ↔ i ∈ Finset.image it.succ.succAbove Sδ ∪ {it.succ}

Tactic:
obtain rfl | ⟨i, rfl⟩ := it.succ.eq_self_or_eq_succAbove i

Goal state after:
case inr.right.inl
m✝ : ℕ
k✝ : Fin (m✝ + 1)
n✝ : ℕ
x : (Λ[m✝ + 1, k✝.castSucc].unionProd ∂Δ[n✝]).N
d✝ m : ℕ
k : Fin (m + 1)
n d : ℕ
is it : Fin (d + 1)
s : (Δ[m + 1] ⊗ Δ[n]) _⦋d + 1⦌
hs₁ : s ∈ (Δ[m + 1] ⊗ Δ[n]).nonDegenerate (d + 1)
hs₂ : s ∉ (Λ[m + 1, k.castSucc].unionProd ∂Δ[n]).obj (Opposite.op ⦋d + 1⦌)
hs : IsIndex (Subcomplex.N.mk s hs₁ hs₂) ⋯ is.succ
t : (Δ[m + 1] ⊗ Δ[n]) _⦋d + 1⦌
ht₁ : t ∈ (Δ[m + 1] ⊗ Δ[n]).nonDegenerate (d + 1)
ht₂ : t ∉ (Λ[m + 1, k.castSucc].unionProd ∂Δ[n]).obj (Opposite.op ⦋d + 1⦌)
ht : IsIndex (Subcomplex.N.mk t ht₁ ht₂) ⋯ it.succ
h₂ :
  (pairingCore k n).type₂ { x := Subcomplex.N.mk s hs₁ hs₂, d := d, hd := ⋯, index := is, isIndex := hs } <
    (pairingCore k n).type₁ { x := Subcomplex.N.mk t ht₁ ht₂, d := d, hd := ⋯, index := it, isIndex := ht }
h₁ : ¬Subcomplex.N.mk s hs₁ hs₂ = Subcomplex.N.mk t ht₁ ht₂
hf : Mono (SimplexCategory.δ it.succ)
Ss : Finset (Fin ((Subcomplex.N.mk s hs₁ hs₂).dim + 1)) := finset (Subcomplex.N.mk s hs₁ hs₂) ⋯
St : Finset (Fin ((Subcomplex.N.mk t ht₁ ht₂).dim + 1)) := finset (Subcomplex.N.mk t ht₁ ht₂) ⋯
Sδ : Finset (Fin (hs.δ.dim + 1)) := finset hs.δ ⋯
hδ : ∀ (i : Fin (d + 1)), s.1 (is.castSucc.succAbove i) = t.1 (it.succ.succAbove i)
hSs : ∀ (i : Fin (d + 1)), i ∈ Sδ ↔ is.castSucc.succAbove i ∈ Ss
hSt : ∀ (i : Fin (d + 1)), i ∈ Sδ ↔ it.succ.succAbove i ∈ St
⊢ it.succ ∈ St ↔ it.succ ∈ Finset.image it.succ.succAbove Sδ ∪ {it.succ}

case inr.right.inr
m✝ : ℕ
k✝ : Fin (m✝ + 1)
n✝ : ℕ
x : (Λ[m✝ + 1, k✝.castSucc].unionProd ∂Δ[n✝]).N
d✝ m : ℕ
k : Fin (m + 1)
n d : ℕ
is it : Fin (d + 1)
s : (Δ[m + 1] ⊗ Δ[n]) _⦋d + 1⦌
hs₁ : s ∈ (Δ[m + 1] ⊗ Δ[n]).nonDegenerate (d + 1)
hs₂ : s ∉ (Λ[m + 1, k.castSucc].unionProd ∂Δ[n]).obj (Opposite.op ⦋d + 1⦌)
hs : IsIndex (Subcomplex.N.mk s hs₁ hs₂) ⋯ is.succ
t : (Δ[m + 1] ⊗ Δ[n]) _⦋d + 1⦌
ht₁ : t ∈ (Δ[m + 1] ⊗ Δ[n]).nonDegenerate (d + 1)
ht₂ : t ∉ (Λ[m + 1, k.castSucc].unionProd ∂Δ[n]).obj (Opposite.op ⦋d + 1⦌)
ht : IsIndex (Subcomplex.N.mk t ht₁ ht₂) ⋯ it.succ
h₂ :
  (pairingCore k n).type₂ { x := Subcomplex.N.mk s hs₁ hs₂, d := d, hd := ⋯, index := is, isIndex := hs } <
    (pairingCore k n).type₁ { x := Subcomplex.N.mk t ht₁ ht₂, d := d, hd := ⋯, index := it, isIndex := ht }
h₁ : ¬Subcomplex.N.mk s hs₁ hs₂ = Subcomplex.N.mk t ht₁ ht₂
hf : Mono (SimplexCategory.δ it.succ)
Ss : Finset (Fin ((Subcomplex.N.mk s hs₁ hs₂).dim + 1)) := finset (Subcomplex.N.mk s hs₁ hs₂) ⋯
St : Finset (Fin ((Subcomplex.N.mk t ht₁ ht₂).dim + 1)) := finset (Subcomplex.N.mk t ht₁ ht₂) ⋯
Sδ : Finset (Fin (hs.δ.dim + 1)) := finset hs.δ ⋯
hδ : ∀ (i : Fin (d + 1)), s.1 (is.castSucc.succAbove i) = t.1 (it.succ.succAbove i)
hSs : ∀ (i : Fin (d + 1)), i ∈ Sδ ↔ is.castSucc.succAbove i ∈ Ss
hSt : ∀ (i : Fin (d + 1)), i ∈ Sδ ↔ it.succ.succAbove i ∈ St
i : Fin (d + 1)
⊢ it.succ.succAbove i ∈ St ↔ it.succ.succAbove i ∈ Finset.image it.succ.succAbove Sδ ∪ {it.succ}