set enable_seqscan=off;
CREATE TABLE test_varchar (
	i varchar
);
INSERT INTO test_varchar VALUES ('a'),('ab'),('abc'),('abb'),('axy'),('xyz');
CREATE INDEX idx_varchar ON test_varchar USING rum (i);
SELECT * FROM test_varchar WHERE i<'abc'::varchar ORDER BY i;
  i  
-----
 a
 ab
 abb
(3 rows)

SELECT * FROM test_varchar WHERE i<='abc'::varchar ORDER BY i;
  i  
-----
 a
 ab
 abb
 abc
(4 rows)

SELECT * FROM test_varchar WHERE i='abc'::varchar ORDER BY i;
  i  
-----
 abc
(1 row)

SELECT * FROM test_varchar WHERE i>='abc'::varchar ORDER BY i;
  i  
-----
 abc
 axy
 xyz
(3 rows)

SELECT * FROM test_varchar WHERE i>'abc'::varchar ORDER BY i;
  i  
-----
 axy
 xyz
(2 rows)