title: ORA-00907: missing right parenthesis i cant find the mistake
body: <pre><code>create table book_copies(
          book_id integer references book(book_id) on delete cascade, 
          programme_id varchar2(20) references library programme(programme_id) on delete cascade,
          nof_copies integer, 
          primary key(book_id,programme_id)
      );
  </code></pre>