Find out the indexed columns

Hi All,
I have a condition based index created. I see that the postgres metadata
table doesn't return columns associated with condition based indexes.

Example:
ssdb=# SELECT indexdef FROM pg_indexes WHERE indexname = 'test_u01';
indexdef
------------------------------------------------------------------
CREATE UNIQUE INDEX test_idx1 ON test USING btree ((+
CASE inet_type +
WHEN 2 THEN a +
WHEN 4 THEN a +
ELSE NULL::character varying +
END), ( +
CASE inet_type +
WHEN 2 THEN ipaddress +
WHEN 4 THEN ipaddress +
ELSE NULL::character varying +
END), ( +
CASE inet_type +
WHEN 2 THEN port +
WHEN 4 THEN port +
ELSE NULL::bigint +
END))
(1 row)

The below query is unable to find the indexed columns (a,ipadress,port)
through the metadata tables for the above expression based index.

SELECT ix.indisprimary as contype,pg_get_userbyid(t.relowner) as
table_owner, t.relname as table_name, pg_get_userbyid(i.relowner) as
index_owner, i.relname as index_name, a.attname as att_name,
pg_catalog.format_type(a.atttypid, a.atttypmod) AS data_type FROM pg_class
t, pg_class i, pg_index ix, pg_attribute a WHERE t.oid = ix.indrelid AND
i.oid = ix.indexrelid AND a.attrelid = t.oid AND a.attnum = ANY(ix.indkey)
AND i.relname = 'test_idx1';

How do I find out the associated columns for such an index?

Regards,
nik