simpa[-cast_fintypeEquivFin_fin] using this.symm
ι : Type u_1
inst✝² : Fintype ι
inst✝¹ : DecidableEq ι
inst✝ : Encodable ι
k : ℕ
i : Fin k
this :
  (fun j => fintypeEquivFin.symm (Fin.cast ⋯ j)) (Fin.cast ⋯ (fintypeEquivFin i)) =
    (fun j => fintypeEquivFin.symm (Fin.cast ⋯ j)) i
⊢ fintypeEquivFin.symm (Fin.cast ⋯ i) = i
no goals