Definition app_2_n {T:Type} {n:nat} (pred : arity T (S (S n))) (x1 x2 : T) (cp : cartesianPower T n) : Prop.

Lemma NoDup_dec {A : Type} : forall (l : list A), (forall x y : A, {x = y} + {x <> y}) -> NoDup l \/ ~ NoDup l.