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Section Definitions.
Definition eq_dec X := forall x y : X, {x=y} + {x <> y}.
Existing Class eq_dec.
(* Any function that uses eq_dec. Doesn't matter -- ↓ ↓ ↓ *)
Definition f {X: Type} {DecX: eq_dec X} (x y: X) := x = y.
End Definitions.
Section MySection.
Context {T: Type}.
Hypothesis TEqDec: eq_dec T.
Inductive myType :=
| C: T -> myType.
Instance myTypeEqDec : eq_dec myType.
Proof. ... Defined.
(* Everything is ok *)
Example example1: forall (t1 t2: myType), f t1 t2.
Proof. ... Qed.
End MySection.
Section AnotherSection.
Context {T: Type}.
Hypothesis TEqDec: eq_dec T.
(* Now I must explicitly specify this -- ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
Example example2: forall (t1 t2: @myType T), @f _ (@myTypeEqDec _ TEqDec) t1 t2.
Proof. ... Qed.
End AnotherSection.
正如您在example1中看到的,Coq能够找到关于myType的实例信息。但是在我改变这个部分之后,关于实例的所有信息都消失了,我必须明确地指定它。所以,当我有很多类型和实例时,代码很快就会变得混乱。很显然,我应该以某种方式将这些信息回复到上下文中。这样做的正确方法是什么?Coq:导入关于实例的信息