Problems with where rownum = 2, but not rownum = 1.

Question

Can anyone explain to me why I get the expected result when I do
rownum = 1
rownum <= 2
rownum < 3
but not for
rownum > 1
rownum = 2
SQL> create table test(a number, b number);
Table created.
SQL> insert into test VALUES(1,2);
1 row created.
SQL> insert into test VALUES(2,3);
1 row created.
SQL> select rownum, a, b from (select a,b from test where a < 10 order by b desc);
ROWNUM A B
1 2 3
2 1 2
SQL> select rownum, a, b from (select a,b from test where a < 10 order by b desc) where rownum = 1;
ROWNUM A B
1 2 3
SQL> select rownum, a, b from (select a,b from test where a < 10 order by b desc) where rownum > 1;
no rows selected
SQL> select rownum, a, b from (select a,b from test where a < 10 order by b desc) where rownum = 2;
no rows selected
SQL> select rownum, a, b from (select a,b from test where a < 10 order by b desc) where rownum <= 2;
ROWNUM A B
1 2 3
2 1 2
SQL> select rownum, a, b from (select a,b from test where a < 10 order by b desc) where rownum < 3;
ROWNUM A B
1 2 3
2 1 2
SQL>

Answer 1

ROWNUM is only incremented when a record passes the WHERE clause (but ROWNUM is assigned before the rows are ordered).
http://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14200/pseudocolumns009.htm#i1006297
So if you need to use a lower bound for ROWNUM, you must use a subquery. And as you usually need first/second/third record when sorting by field x, there will be two levels of subqueries.
SELECT *
FROM (SELECT *, rownum rn
FROM (SELECT ...your query... ORDER BY x)
WHERE rownum<=2
WHERE rn=2