Inductive trunc : nat -> List -> List -> Prop :=
    | trunc_O : forall e : List, trunc 0 e e
    | trunc_S :
        forall (k : nat) (e f : List) (x : A),
        trunc k e f -> trunc (S k) (x :: e) f.Inductive trunc : nat -> List -> List -> Prop :=
    | trunc_O : forall e : List, trunc 0 e e
    | trunc_S :
        forall (k : nat) (e f : List) (x : A),
        trunc k e f -> trunc (S k) (x :: e) f.Inductive trunc : nat -> List -> List -> Prop :=
    | trunc_O : forall e : List, trunc 0 e e
    | trunc_S :
        forall (k : nat) (e f : List) (x : A),
        trunc k e f -> trunc (S k) (x :: e) f.

Lemma item_trunc : forall (n : nat) (e : List) (t : A), item t e n -> exists f : List, trunc (S n) e f.