This is the fourth volume of papers presented at the New York Number Theory Semlnar. Since 1982 the Seminar has been meeting every Tuesday afternoon during the academic year at the Graduate School and University Center of the City University of New York. The goal of the Seminar is to provide a forum for the exposure of new results in number theory and allied fields in the New York metropolitan area. Mathematicians who plan to be in New York and would I like to attend or lecture in the Seminar are encouraged to contact the organizers.