Error, while using aggregated functions/window functions in anchor part

create table t1(b int);

insert into t1 values(10),(20),(10);

with recursive qn as

  (select max(b) as a from t1 union

   select a from qn)

select * from qn;

with recursive qn as

  (select rank() over (order by b) as a from t1 union

   select a from qn)

select * from qn;