Record dynamic : Type := dyn {typ : Type; val : typ}.Record dynamic : Type := dyn {typ : Type; val : typ}.Record dynamic : Type := dyn {typ : Type; val : typ}.Record dynamic : Type := dyn {typ : Type; val : typ}.Notation dynamic := Dyn.dynamic.Notation dyn := Dyn.dyn.

Lemma dyn_inj A (x y : A) : dyn x = dyn y -> x = y.