&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Bulletin (New Series) of the American Mathematical Society. 1986.<br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Vol. 15 No. 1 : Vol. 15 No. 1. &mdash; 1986. &mdash; ISSN 0273-0979.<br><br><br><br>[ SYS NUM: 15698 ]