Definition active_term_order_superset_dec: forall (t t': active_term), {active_term_order_superset t t'} + {~ active_term_order_superset t t'}.Definition lex : (active_term * term) -> (active_term * term) -> Prop :=
  lexprod active_term_order_superset term_order.

Lemma sub_terms_trans t1 t2 t3: In t1 (sub_terms variable function constructor t2) -> In t2 (sub_terms _ _ _ t3) -> In t1 (sub_terms _ _ _ t3).