congr 2
case succ
k✝ : Nat
α : Type u_1
f : Fin k✝ → α
i✝ j i : Nat
h : i + 1 + j = k✝
k : Nat
hk : k + 1 < (ofFn.go f (i + 1) j h).length
⊢ f ⟨j + 1 + k, ⋯⟩ = f ⟨j + (k + 1), ⋯⟩
case succ.e_a.e_val
k✝ : Nat
α : Type u_1
f : Fin k✝ → α
i✝ j i : Nat
h : i + 1 + j = k✝
k : Nat
hk : k + 1 < (ofFn.go f (i + 1) j h).length
⊢ j + 1 + k = j + (k + 1)