(* TODO: try to see if using sorted lists would not make the tactic faster. *)
Definition STelt := tST.
Definition STt := list tST.
Definition STempty : STt := nil.

Lemma eqST_dec : forall x y, {eqST x y} + {~ eqST x y}.
Definition STadd (x : STelt) (s : STt) := cons x s.