fact: Fixpoint fresh (L : vars) (n : nat) (xs : list var) {struct xs} : Prop := match xs, n with | nil, O => True | x::xs', S n' => x \notin L /\ fresh (L \u \{x}) n' xs' | _,_ => False end.
imports: TLC(LibTactics LibList LibLogic LibNat LibEpsilon LibReflect)