set enable_seqscan=off;
CREATE TYPE rainbow AS ENUM ('r','o','y','g','b','i','v');
CREATE TABLE test_enum (
   i rainbow
);
INSERT INTO test_enum VALUES ('v'),('y'),('r'),('g'),('o'),('i'),('b');
CREATE INDEX idx_enum ON test_enum USING gin (i);
SELECT * FROM test_enum WHERE i<'g'::rainbow ORDER BY i;
 i 
---
 r
 o
 y
(3 rows)

SELECT * FROM test_enum WHERE i<='g'::rainbow ORDER BY i;
 i 
---
 r
 o
 y
 g
(4 rows)

SELECT * FROM test_enum WHERE i='g'::rainbow ORDER BY i;
 i 
---
 g
(1 row)

SELECT * FROM test_enum WHERE i>='g'::rainbow ORDER BY i;
 i 
---
 g
 b
 i
 v
(4 rows)

SELECT * FROM test_enum WHERE i>'g'::rainbow ORDER BY i;
 i 
---
 b
 i
 v
(3 rows)

explain (costs off) SELECT * FROM test_enum WHERE i>='g'::rainbow ORDER BY i;
                  QUERY PLAN                   
-----------------------------------------------
 Sort
   Sort Key: i
   ->  Bitmap Heap Scan on test_enum
         Recheck Cond: (i >= 'g'::rainbow)
         ->  Bitmap Index Scan on idx_enum
               Index Cond: (i >= 'g'::rainbow)
(6 rows)

-- make sure we handle the non-evenly-numbered oid case for enums
create type e as enum ('0', '2', '3');
alter type e add value '1' after '0';
create table t as select (i % 4)::text::e from generate_series(0, 100000) as i;
create index on t using gin (e);