coq - Coq：活页夹下的参数重写

Question

我有一个参数关系，只要两者都与相同的参数一起使用myeq，我想在谓词下重写。P如果我声明适当的态射，它会很好地工作：

From Coq Require Import Setoid Morphisms.

Parameter A B : Type.
Parameter myeq : A -> relation B.
Add Parametric Relation (a : A) : B (myeq a) as myeq_rel.

Parameter P : A -> B -> Prop.
Add Parametric Morphism (a : A) : (P a)
    with signature (myeq a) ==> iff as P_morphism.
Admitted.

Lemma test1 b1 b2 :
  (forall a, myeq a b1 b2) ->
  exists a, P a b1.
Proof.
  intro.
  setoid_rewrite H. (* OK *)
Abort.

然而，当我尝试应用一个函数时它停止工作，甚至注册为一个态射myeq：

Parameter Op : B -> B.
Add Parametric Morphism (a : A) : Op
    with signature (myeq a) ==> (myeq a) as op_morphism.
Admitted.

Lemma test2 b1 b2 :
  (forall a, myeq a b1 b2) ->
  exists a, P a (Op b1).
Proof.
  intro.
  setoid_rewrite H. (* not OK, why? *)
Abort.

我忘了申报什么吗？