Definition term_from_active_term (t: active_term) : term :=
let (f, lv) := t in
fapply f (map (@term_from_value _ _ _) lv).
Definition value_list_order (lv lv' : list value) : Prop :=
suml (map (@value_size _) lv) < suml (map (@value_size _) lv').

Lemma unify_list_sound :
forall (lp : list pattern) (lv : list value) (s : variable -> value),
unify_list [] lv lp = Some s -> map (psubst s) lp = lv.