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| Inductive Vector (A : Type) : nat -> Type := | |
| | nil : Vector A O | |
| | cons : forall n, A -> Vector A n -> Vector A (S n). | |
| Definition head (A : Type) (n : nat) (v : Vector A (S n)) : A. | |
| refine ( | |
| (match v in Vector _ m return m = S n -> A with | |
| | nil => _ | |
| | cons _ hd tl => fun _ => hd | |
| end) (eq_refl (S n))). | |
| inversion 1. | |
| Defined. |
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