SELECT DISTINCT on boxes

Is there a way to do a SELECT DISTINCT on boxes:

test=> create TABLE t3 (a box);
CREATE TABLE
test=> insert into t3 values ('(2,2),(1,1)');
INSERT 17232 1
test=> insert into t3 values ('(2,2),(1,1)');
INSERT 17233 1
test=> insert into t3 values ('(3,3),(2,2)');
INSERT 17234 1
test=> insert into t3 values ('(3,3),(2,2)');
INSERT 17235 1
test=> select distinct * from t3;
ERROR: could not identify an ordering operator for type box
HINT: Use an explicit ordering operator or modify the query.

I tried doing subqueries and using oids but that didn't help.

I don't understand why this doesn't work:

SELECT a
FROM t3 t2
WHERE t2.oid = (SELECT MIN(t.oid) FROM t3 t WHERE t2.a = t.a);

a
-------------
(2,2),(1,1)
(1 row)

If finds only the duplicate.

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