Same expression more than once in partition key

Hi,

When we create a range partitioned table, we cannot use
a column more than once in the partition key.

postgres=# create table t (i int) partition by range(i,i);
ERROR: column "i" appears more than once in partition key

However, I can use same expression more than once in partition key.

postgres=# create table t (i int) partition by range((i),(i));
CREATE TABLE

Although this can be blocked by the attached parch, for example,
the following is still possible.

postgres=# create table t (i int) partition by range((i),i);
CREATE TABLE

Can these definition be a problem in the internal of partitioning?
If not, we might not need to check column that apears more than once
in the partition key.

Regards,

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>