(** * Definitions *)

Definition symbol := nat.Definition string := (string nat).Definition card : Type := (card nat).Definition stack := stack nat.Notation "x / y" := (x,y).Implicit Types a b : symbol.Implicit Types x y z : string.Implicit Types d e : card.Implicit Types A R P : stack.

Lemma tau2_app A B : tau2 (A ++ B) = tau2 A ++ tau2 B.