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CONTEMPORARY MATHEMATICS 229 Trends in the Representation Theory of Finite Dimensional Algebras 1997 Joint Summer Research Conference on Trends in the Representation Theory of Finite Dimensional Algebras July 2Q-24, 1997 Seattle, Washington Edward L. Green Birge Huisgen-Zimmermann Editors http://dx.doi.org/10.1090/conm/229 Selected Titles in This Series 229 Edward L. Green and Birge Huisgen-Zimmermann, Editors, Trends in the representation theory of finite dimensional algebras, 1998 228 Liming Ge, Huaxin Lin, Zhong-Jin Ruan, Dianzhou Zhang, and Shuang Zhang, Editors, Operator algebras and operator theory, 1999 227 John McCleary, Editor, Higher homotopy structures in topology and mathematical physics, 1999 226 Luis A. Caffarelli and Mario Milman, Editors, Monge Ampere equation: Applications to geometry and optimization, 1999 225 Ronald C. Mullin and Gary L. Mullen, Editors, Finite fields: Theory, applications, and algorithms, 1999 224 Sang Geun Hahn, Hyo Chul Myung, and Efim Zelmanov, Editors, Recent progress in algebra, 1999 223 Bernard Chazelle, Jacob E. Goodman, and Richard Pollack, Editors, Advances in discrete and computational geometry, 1999 222 Kang-Tae Kim and Steven G. Krantz, Editors, Complex geometric analysis in Pohang, 1999 221 J. Robert Dorroh, Gisele Ruiz Goldstein, Jerome A. Goldstein, and Michael Mudi Tom, Editors, Applied analysis, 1999 220 Mark Mahowald and Stewart Priddy, Editors, Homotopy theory via algebraic geometry and group representations, 1998 219 Marc Henneaux, Joseph Krasil'shchik, and Alexandre Vinogradov, Editors, Secondary calculus and cohomological physics, 1998 218 Jan Mandel, Charbel Farhat, and Xiao-Chuan Cai, Editors, Domain decomposition methods 10, 1998 217 Eric Carlen, Evans M. Harrell, and Michael Loss, Editors, Advances in differential equations and mathematical physics, 1998 216 Akram Aldroubi and EnBing Lin, Editors, Wavelets, multiwavelets, and their applications, 1998 215 M. G. Nerurkar, D.P. Dokken, and D. B. Ellis, Editors, Topological dynamics and applications, 1998 214 Lewis A. Coburn and Marc A. Rieffel, Editors, Perspectives on quantization, 1998 213 Farhad Jafari, Barbara D. MacCluer, Carl C. Cowen, and A. Duane Porter, Editors, Studies on composition operators, 1998 212 E. Ramirez de Arellano, N. Salinas, M. V. Shapiro, and N. L. Vasilevski, Editors, Operator theory for complex and hypercomplex analysis, 1998 211 Jozef Dodziuk and Linda Keen, Editors, Lipa's legacy: Proceedings from the Bers Colloquium, 1997 210 V. Kumar Murty and Michel Waldschmidt, Editors, Number theory, 1998 209 Steven Cox and Irena Lasiecka, Editors, Optimization methods in partial differential equations, 1997 208 Michel L. Lapidus, Lawrence H. Harper, and Adolfo J. Rumbos, Editors, Harmonic analysis and nonlinear differential equations: A volume in honor of Victor L. Shapiro, 1997 207 Yujiro Kawamata and Vyacheslav V. Shokurov, Editors, Birational algebraic geometry: A conference on algebraic geometry in memory of Wei-Liang Chow (1911-1995), 1997 206 Adam Koranyi, Editor, Harmonic functions on trees and buildings, 1997 205 Paulo D. Cordaro and Howard Jacobowitz, Editors, Multidimensional complex analysis and partial differential equations: A collection of papers in honor of Fran<;ois Treves, 1997 (Continued in the back of this publication) Trends in the Representation Theory of Finite Dimensional Algebras CoNTEMPORARY MATHEMATICS 229 Trends in the Representation Theory of Finite Dimensional Algebras 1997 Joint Summer Research Conference on Trends in the Representation Theory of Finite Dimensional Algebras July 20-24, 1997 Seattle, Washington Edward L. Green Birge Huisgen-Zimmermann Editors American Mathematical Society Providence, Rhode Island Editorial Board Dennis DeTurck, managing editor Andy R. Magid Michael Vogelius Clark Robinson Peter M. Winkler The 1997 AMS-IMS-SIAM Joint Summer Research Conference in the Mathematical Sciences on "Trends in the Representation Theory of Finite Dimensional Algebras" was held at the University of Washington on July 2Q-24, 1997, with support from the Na- tional Science Foundation, Grant DMS-9618514, and the National Security Agency, Grant MDA904-97-1-0071. 1991 Mathematics Subject Classification. Primary 14D15, 14130, 16D30, 16D60, 16E10, 16E30, 16E40, 16G10, 16G20, 16G30, 16G50, 16G60, 16G70, 16P10, 16P20, 16P40, 16S80, 16W30, 17B37, 81R50. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Library of Congress Cataloging-in-Publication Data Trends in the representation theory of finite dimensional algebras : proceedings of the AMS- IMS-SIAM joint summer research conference, trends in the representation theory of finite dimen- sional algebras, July 20-24, 1997, University of Washington / Edward L. Green, Birge Huisgen- Zimmermann, editors. p. em. - (Contemporary mathematics, ISSN 0271-4132 ; 229) Includes bibliographical references. ISBN 0-8218-0928-8 (soft : alk. paper) 1. Associative algebras-Congresses. 2. Representations of algebras-Congresses. I. Green, Edward L., [DATE]. II. Huisgen-Zimmermann, Birge, [DATE]. III. Series: Contemporary mathematics (American Mathematical Society) : v. 229. QA251.5.T74 1998 512'.24--dc21 98-44526 CIP Copying and reprinting. Material in this book may be reproduced by any means for educational and scientific purposes without fee or permission with the exception of reproduction by services that collect fees for delivery of documents and provided that the customary acknowledgment of the source is given. This consent does not extend to other kinds of copying for general distribution, for advertising or promotional purposes, or for resale. Requests for permission for commercial use of material should be addressed to the Assistant to the Publisher, American Mathematical Society, P. 0. Box 6248, Providence, Rhode Island 02940-6248. Requests can also be made by e-mail to reprint-permission~ams.org. Excluded from these provisions is material in articles for which the author holds copyright. In such cases, requests for permission to use or reprint should be addressed directly to the author(s). (Copyright ownership is indicated in the notice in the lower right-hand corner of the first page of each article.) @J 1998 by the American Mathematical Society. All rights reserved. The American Mathematical Society retains all rights except those granted to the United States Government. Printed in the United States of America. § The paper used in this book is acid-free and falls within the guidelines established to ensure permanence and durability. Visit the AMS home page at URL: http: I /www. ams. org/ 10 9 8 7 6 5 4 3 2 1 03 02 01 00 99 98 Contents Preface IX List of Talks xi Postprojective partitions for tilting torsion pairs I. ASS EM AND F. U. COELHO 1 Derived canonical algebras as one-point extensions M. BAROT AND H. LENZING 7 Special biserial algebras and their automorphisms F. M. BLEHER 17 Wild subquivers of the Auslander-Reiten quiver of a tame algebra S. BRENNER AND M. C. R. BUTLER 29 Representation theory of noetherian Hopf algebras satisfying a polynomial identity K. A. BROWN 49 Finite representation type and periodic Hochschild (co-)homology R.-0. BUCHWEITZ 81 The syzygy theorem for monomial algebras M. C. R. BUTLER 111 Algebras whose derived category is tame J. A. DELAPENA 117 Circular biextensions of tame concealed algebras P. DRAXLER 129 On the distribution of AR-components of restricted Lie algebras R. FARNSTEINER 139 Compatible deformations M. GERSTENHABER AND A. GIAQUINTO 159 Directing objects in hereditary categories D. HAPPEL AND I. REITEN 169 On subcategories associated with tilting modules D. HAPPEL AND L. UNGER 181 vii viii CONTENTS Modules of the highest homological dimension over a Gorenstein ring Y. lWANAGA AND J. MIYACHI 193 Derived equivalence of graph algebras M. KAUER 201 Basic results on wild hereditary algebras 0. KERNER 215 On minimal approximations of modules H. KRAUSE AND M. SAORIN 227 Serre duality for generalized Auslander regular algebras R. MARTINEZ-VILLA 237 Classifying finite-dimensional semisimple Hopf algebras S. MONTGOMERY 265 Geometry of modules: Degenerations CH. RIEDTMANN 281 The preprojective algebra of a tame quiver: The irreducible components of the module varieties C. M. RINGEL 293 Representation types, Tits reduced quadratic forms and orbit problems for lattices over orders D. SIMSON 307 Degenerations in module varieties with finitely many orbits A. SKOWRONSKI AND G. ZWARA 343 Preface The American Mathematical Society, the Institute of Mathematical Statis- tics, and the Society for Industrial and Applied Mathematics sponsored a joint summer research conference at the University of Washington, from July 2D-24, 1997, on Trends in the Representation Theory of Finite Dimensional Algebras. The conference was organized by E. L. Green (Virginia Polytechnic Institute and State University) and B. Huisgen-Zimmermann (University of California at Santa Barbara). The lectures focused on the following three topics: (1) Interactions between representation theory and algebraic geometry; (2) Homological methods; (3) Applications of representation theory to the study of quantum groups. All three lines were strongly represented in the conference by lectures providing keynote reports and talks addressing current research, as well as by contributions to this volume. (1) The analysis of representations via algebraic varieties is comparatively young. It goes back to the 1970's,