______CHELSEA SCIENTIFIC BOOKS______ THE PROBLEM OF PLATEAU, By T. Rado. 1933. 113 pages. 5j4x8. Cloth. Originally publ. (in paper binding) at $5.10. $2.95 From Ergebnisse der Mathematik. EINFUEHRUNG IN DIE KOMBINA-TORISCHE TOPOLOGIE, By K. Reide- meister. 221 pages. 5^x8^. $3.95 Group Theory occupies the first half of the book; applications to Topology, the second. This well-known book is of interest both to algebraists and topologists. KNOTENTHEORIE, By K. Reidemeister. 1932. 78 pages. 5j4x854. $2.25 "well written . . . the problem is ... fascinating. The complete and concise little work of Reidemeister will do much to encourage further. [research]."—Bulletin of ike American Mathematical Society. FOURIER SERIES, By W. Rogosinski. 1950. 182 pp. 4*4x6^ inches. (English translation). $2.50 This text, designed for beginners with no more background than a year of calculus, covers, nevertheless, an amazing amount of ground. It is suitable for self-study courses as well as classroom use. "Up to modern standards and, at the same time, suitable for beginners."—F. Riess, Ada Sseged. INTRODUCTION TO MODERN ALGEBRA AND MATRIX THEORY, By O. Schreier and E. Sperner. About 400 pp. 6x9. (Summer, 1951) $4.95 An English translation of the revolutionary work, Einfilhrung in die Analytische Geometric und Algebra. Chapter Headings: I. Affine Space. Linear Equations. (Vector Spaces). II. Euclidean Space. Theory of Determinants. III. The Theory of Fields. Fundamental Theorem of Algebra. IV. Elements of Group Theory. V. Matrices and Linear Transformations. The treatment of matrices is especially extensive. LEHRBUCH DER TOPOLOGIE, By H. Seifert and W. Threlfall. 1934. 360 pages. 5^x8^4. Originally published at $8.00. $4.50 This famous book is the only modern work on com-binatorial topology addressed to the student as well as to the specialist. It is almost indispensable to the mathematician who wishes to gain a knowledge of this important field.