[HACKERS] "cannot specify finite value after UNBOUNDED" ... uh, why?

Would someone please defend the restrictions imposed by the
"seen_unbounded" checks in transformPartitionBound
(parse_utilcmd.c:3365..3396 in current HEAD)?  They sure look to me like
nothing but sloppy thinking, and/or protection of downstream sloppy
thinking.  Why should the boundedness of one partitioning column's
range matter to any other partitioning column's range?
        regards, tom lane