rfl
case refine_2.h
m n : Nat
l : List (Fin (n + 1))
h : ¬last n ∈ l
i : Nat
hi : i < List.length l
h₂✝ :
  i <
    List.length
      (List.map castSucc
        (List.pmap (fun i hi => { val := ↑i, isLt := hi }) l (_ : ∀ (i : Fin (n + 1)), i ∈ l → ↑i < n)))
⊢ List.get l { val := i, isLt := hi } =
    castSucc
      {
        val :=
          ↑(List.get l
              (cast
                (_ :
                  List.length
                      (List.pmap (fun i hi => { val := ↑i, isLt := hi }) l (_ : ∀ (i : Fin (n + 1)), i ∈ l → ↑i < n)) =
                    List.length l)
                { val := ↑{ val := i, isLt := h₂✝ },
                  isLt :=
                    (_ :
                      ↑{ val := i, isLt := h₂✝ } <
                        List.length
                          (List.pmap (fun i hi => { val := ↑i, isLt := hi }) l
                            (_ : ∀ (i : Fin (n + 1)), i ∈ l → ↑i < n))) })),
        isLt :=
          (_ :
            ↑(List.get l
                  (cast
                    (_ :
                      List.length
                          (List.pmap (fun i hi => { val := ↑i, isLt := hi }) l
                            (_ : ∀ (i : Fin (n + 1)), i ∈ l → ↑i < n)) =
                        List.length l)
                    { val := ↑{ val := i, isLt := h₂✝ },
                      isLt :=
                        (_ :
                          ↑{ val := i, isLt := h₂✝ } <
                            List.length
                              (List.pmap (fun i hi => { val := ↑i, isLt := hi }) l
                                (_ : ∀ (i : Fin (n + 1)), i ∈ l → ↑i < n))) })) <
              n) }
no goals