Intersection of two time segments

I'm doing some temporal queries in PostgreSQL and am in need of a way to
find the start/end times for overlapping time segments.

I know about this query, which will tell me whether or not a time
segment overlaps:
select (timestamp '2001-02-01 0:00', timestamp '2001-09-30 0:00')
overlaps (timestamp '2001-01-01 0:00', timestamp '2001-04-30 0:00');

But I would like to know the actual start/end times for the overlapping
segment (i.e. 2002-02-01 to 2001-04-30).  Is there something already
available that will do that, or do I have to write a function to do this?

Thanks!

-Jon