&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Bulletin (New Series) of the American Mathematical Society. 1988.<br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Vol. 18 No. 2 : Vol. 18 No. 2. &mdash; 1988. &mdash; ISSN 0273-0979.<br><br><br><br>[ SYS NUM: 15705 ]