create or replace function toset(l) as
  array_sort(list_distinct(l));

create or replace function array_intersection(a,b) as
  array_filter(a, x -> array_contains(b, x));

create or replace function set_union(a,b) as
  toset(toset(a) || toset(b)));

create or replace function set_intersection(a,b) as
  array_intersection(toset(a),toset(b));