proposition: Lemma lazy_append_in_l : forall {B : Type} ll (b : B) l, In_ll b l -> In_ll b (lazy_append l ll).
proof: Proof. intros B ll; induction ll; intros b l0 HIn. - auto using lazy_append_nil_r. - induction l0. + inversion HIn. + simpl in *. firstorder. Qed.
imports: ExtLib.Structures(Functor Applicative) List QuickChick(Tactics) Coq(ssreflect)