Asta.add_top asta top_st;
Asta.add_bot asta top_st; (* for trees which are leaves *)
Asta.add_tr asta (top_st, Asta.any_label, or_top) true
Asta.add_top asta top_st;
Asta.add_bot asta top_st; (* for trees which are leaves *)
Asta.add_tr asta (top_st, Asta.any_label, or_top) true