calc
  _ = fsubst ‹a₁ ≃ a₂› (ctx.ind_diff a₁)         := rfl
  _ = fsubst ‹a₁ ≃ a₂› (fsubst ‹d₁ ≃ a₁› od₁)    := rfl
  _ ≃ fsubst (Rel.trans ‹d₁ ≃ a₁› ‹a₁ ≃ a₂›) od₁ := fsubst_trans
  _ = fsubst ‹d₁ ≃ a₂› od₁                       := rfl
  _ ≃ fsubst ‹d₁ ≃ a₂› (fsubst ‹d₂ ≃ d₁› od₂)    := fsubst_substR od_subst
  _ ≃ fsubst (Rel.trans ‹d₂ ≃ d₁› ‹d₁ ≃ a₂›) od₂ := fsubst_trans
  _ = fsubst ‹d₂ ≃ a₂› od₂                       := rfl
  _ = ctx.ind_diff a₂                            := rfl
ℕ : Type
inst✝¹ : Natural ℕ
motive : Difference ℕ → Sort u
inst✝ : IndexedFamily motive
ctx : Induction.Context motive
n₁ m₁ n₂ m₂ : ℕ
a₁ : Difference ℕ := n₁——m₁
a₂ : Difference ℕ := n₂——m₂
x✝ : a₁ ≃ a₂
d₁ : Difference ℕ := n₁——0 - m₁——0
d₂ : Difference ℕ := n₂——0 - m₂——0
this✝² : d₁ ≃ a₁
this✝¹ : d₂ ≃ a₂
this✝ : d₁ ≃ a₂
this : d₂ ≃ d₁
od₁ : motive (Coe.coe n₁ - Coe.coe m₁) := Induction.Context.on_diff n₁ m₁
od₂ : motive (Coe.coe n₂ - Coe.coe m₂) := Induction.Context.on_diff n₂ m₂
od_subst : od₁ ≃ fsubst this od₂
⊢ fsubst x✝ (Induction.Context.ind_diff ctx a₁) ≃ Induction.Context.ind_diff ctx a₂
no goals