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_injT A1 A2 (x1 : A1) (x2 : A2) : dyn x1 = dyn x2 -> A1 = A2.