处理假设

Question

作为Coq中的练习，我试图证明以下函数返回一对长度相等的列表。

Require Import List.

Fixpoint split (A B:Set)(x:list (A*B)) : (list A)*(list B) :=
match x with
|nil => (nil, nil)
|cons (a,b) x1 => let (ta, tb) := split A B x1 in (a::ta, b::tb)
end.

Theorem split_eq_len : forall (A B:Set)(x:list (A*B))(y:list A)(z:list B),(split A B x)=(y,z) -> length y = length z.
Proof.
intros A B x.
elim x.
simpl.
intros y z.
intros H.
injection H.
intros H1 H2.
rewrite <- H1.
rewrite <- H2.
reflexivity.
intros hx.
elim hx.
intros a b tx H y z.
simpl.
intro.

在最后一步之后，我得到一个内部有let语句的假设，我不知道如何处理：

1 subgoals
A : Set
B : Set
x : list (A * B)
hx : A * B
a : A
b : B
tx : list (A * B)
H : forall (y : list A) (z : list B),
    split A B tx = (y, z) -> length y = length z
y : list A
z : list B
H0 : (let (ta, tb) := split A B tx in (a :: ta, b :: tb)) = (y, z)
______________________________________(1/1)
length y = length z

Answer 1

你想做destruct (split A B tx)。这会将其分解，将两个部分绑定到ta和tb