Module: Mathlib.AlgebraicTopology.SimplicialSet.AnodyneExtensions.UnionProd

Goal state before:
pp: case 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)
hδ :
  (ConcreteCategory.hom ((Δ[m + 1] ⊗ Δ[n]).map (SimplexCategory.δ it.succ).op))
      ((pairingCore k n).type₁
          { x := Subcomplex.N.mk t ht₁ ht₂, d := d, hd := ⋯, index := it, isIndex := ht }).simplex =
    ((pairingCore k n).type₂ { x := Subcomplex.N.mk s hs₁ hs₂, d := d, hd := ⋯, index := is, isIndex := hs }).simplex
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 ⋯
⊢ (finset { x := Subcomplex.N.mk s hs₁ hs₂, d := d, hd := ⋯, index := is, isIndex := hs }.x ⋯).card <
    (finset { x := Subcomplex.N.mk t ht₁ ht₂, d := d, hd := ⋯, index := it, isIndex := ht }.x ⋯).card

Tactic:
replace hδ (i : Fin (d + 1)) :
          s.1 (is.castSucc.succAbove i) = t.1 (it.succ.succAbove i) :=
        DFunLike.congr_fun (congr_arg Prod.fst hδ.symm) i

Goal state after:
case 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)
⊢ (finset { x := Subcomplex.N.mk s hs₁ hs₂, d := d, hd := ⋯, index := is, isIndex := hs }.x ⋯).card <
    (finset { x := Subcomplex.N.mk t ht₁ ht₂, d := d, hd := ⋯, index := it, isIndex := ht }.x ⋯).card