setting up foreign keys

Hi all,

This is my first post to the performance list, I hope someone can help me.

I'm setting up a table with 2 columns, both of which reference a column
in another table:

CREATE TABLE headwords_core_lexemes (
core_id int REFERENCES headwords_core(core_id),
lexeme_id int REFERENCES headwords_core(core_id),
);

Trouble is, it's taken 18 hours and counting!  The table headwords_core
only has about 13,000 lines, and core_id is the primary key on that
table. However, I assume it must be those 13,000 lines that are the
problem, since if I try it referencing a similar table with 360 lines
the new table is created almost instantly.

I found a post on a similar subject from quite a while ago, but no
answer, and that was for millions of rows anyway. I only have 13,000.
Surely it should be faster than this? Is there a way to speed it up?

Sue Fitt