Definition ltF : list Tree -> list Tree -> Prop := fun f' => fun f => exists w, exists a,
is_insert_forest f w a f'  /\ (forall t, tree_in_forest t f' -> bad_seq_in_lbl t) /\ f<>f'.
Fact acc_ltF_nil : Acc ltF nil.
constructor; intros f Hf.
elim Hf; clear Hf; intros w H; elim H; clear H; intros a H;
elim H; clear H; intros H1 H; elim H; clear H; intros H2 H3.
inversion H1; subst.
elim H3; trivial.
Qed.
Fact acc_ltF_cons : forall f t, Acc ltF f -> Acc ltF (t::nil) -> Acc ltF (t::f).

Lemma acc_ltF_single : forall ws, Acc (continues embeds) ws ->
forall l a bs, Acc (continues leA) bs ->
forall ts, Acc ltF ts ->
forall t, root t = (ws,a::l) /\ subtrees t = ts /\ Some bs = roots_labels ts ->
Acc ltF (t::nil).