AW: PLEASE help with foreign key and inheritance proble m

I stated this before, but I did not get a helpful answer. I
might have
misunderstood tghe documentation on foreign keys:

create table global(id serial);
create table child(anything text) inherits(global);

need:
create unique index child_id_index on child (id);

gives me an error:
CREATE TABLE will create implicit trigger(s) for FOREIGN KEY check(s)
ERROR: UNIQUE constraint matching given keys for referenced
table "child"
not found

Then the above works.
Actually the error message sounds sufficiently clear to me, no?

Andreas