infinity as a date

I see that Postgres has a special keyword "infinity" for use with
timestamps. Is there an equivalent for dates?

It seems I can set a date field to be 'infinity'::timestamp, but I can't
find a way to then query a table for fields that are 'infinity' ...

I tried the following but it doesn't quite work:

JC=# create table test(a date);
CREATE TABLE
JC=# insert into test values('infinity'::timestamp);
INSERT 1030323 1
JC=# select * from test;
a
---

(1 row)

JC=# select * from test where a='infinity'::timestamp;
a
---
(0 rows)

Is there a correct way to represent a date that is "later/earlier than
any other date"?

Thanks!

Jc