Question

我在实现简单功能方面遇到了问题，我很确定答案是“护航模式”，但我无法弄清楚如何在这种特殊情况下应用它。这是一个完整的例子：

Require Import Coq.Lists.List.

Definition index_map_spec (domain range: nat) :=
  forall n : nat, n < domain -> {v : nat | v < range}.

Lemma lt_pred_l {n m} (H: S n < m): n < m.
Proof. auto with arith. Defined.

Fixpoint natrange_f_spec
         (n:nat)
         {i o: nat}
         (nd: n<i)
         (f_spec: index_map_spec i o)
  : list nat
  :=
    match n return list nat with
    | 0 => nil
    | S n' => cons n' (natrange_f_spec n' (lt_pred_l nd) f_spec)
    end.

我得到的错误是：

The term "nd" has type "n < i" while it is expected to have type
 "S ?578 < ?579".

所以基本上我想在'n'上匹配（n = S p）它会重写（n

Answer 1

您只需抽象nd上的match证明，相应地更改其返回类型：

Require Import Coq.Lists.List.

Definition index_map_spec (domain range: nat) :=
  forall n : nat, n < domain -> {v : nat | v < range}.

Lemma lt_pred_l {n m} (H: S n < m): n < m.
Proof. auto with arith. Defined.

Fixpoint natrange_f_spec
         (n:nat)
         {i o: nat}
         (nd: n<i)
         (f_spec: index_map_spec i o)
  : list nat
  :=
    match n return n < i -> list nat with
    | 0 => fun _ => nil
    | S n' => fun nd => cons n' (natrange_f_spec n' (lt_pred_l nd) f_spec)
    end nd.

车队模式和比赛涉及不平等

1 个答案: