Merrill, William Stetson Code for classifiers : principles governing the consistent placing of books in a system of classification / William Stetson Merrill - 2nd ed. - Chicago : American library association , 1939 - xi, [1], 177 p., 1 l. ; 21 cm. Includes bibliographical references and index. Subjects--Topical Terms: Classification--Books Dewey Class. No.: 020 / MER