Martin Gardner PENROSE TILES TO TRHPDOOR CIPHERS ... OF DR. MATRIX The Mathematical Association of America Washington, D.C. Cover design by John Johnson, Teapot Graphics @ 1989 by W. H. Freeman This book was updated and revised from the 1989 edition published by W. H. Freeman, New York @ 1997 by The Mathematical Association of America (Incorporated) Library of Congress Catalog Card Number 97-70505 ISBN 0-88385-521-6 Printed in the United States ofAmerica Current Printing (last digit): 1 0 9 8 7 6 5 4 3 2 1 PENROSE TILES to Trapdoor Ciphers ... and the return of Dr. Matrix SPECTRUM SERIES Published by THE MATHEMATICAL ASSOCIATION OF AMERICA Committee on Publications JAMES W. DANIEL, Chair Spectrum Editorial Board ARTHUR T. BENJAMIN, Editor DANIEL ASIMOV KATHLEEN BERVER DIPA CHOUDHURY RICHARD K. GUY JEFFREY NUNEMACHER ELLEN MAYCOCK PARKER JENNIFER J. QUINN EDWARD R. SCHEINERMAN SANFORD L. SEGAL To Roger Penrose For his beautiful, surprising discoveries in mathematics, physics and cosmology; for his deep creative insight into how the universe operates; and for his humility in not supposing that he is exploring only the PI-oducts of human minds. SPECTRUM SERIES The Spectrum Series of the Mathematical Association of America was so named to reflect its purpose: to publish a broad range of books including biographies, accessible expositions of old or new mathematical ideas, reprints and revisions of excellent out-of-print books, popular works, and other monographs of high interest that will appeal to a broad range of readers, including students and teachers of mathematics, mathematical amateurs, and researchers. All the Math That's Fit to Print, by Keith Devlin Circles: A Mathematical View, by Dan Pedoe Complex Numbers and Geometry, by Liang-shin Hahn Cryptology, by Albrecht Beutelspacher Five Hundred Mathematical Challenges, Edward J. Barbeau, Murray S. Klamkin, and William 0. J. Moser From Zero to Infinity, by Constance Reid I Want to be a Mathematician, by Paul R. Halmos Journey into Geometries, by Marta Sved JULIA: a life in mathematics, by Constance Reid The Last Problem, by E. T. Bell (revised and updated by Underwood Dudley) The Lighter Side of Mathematics: Proceedings of the Eugkne Strens Memorial Confer- ence on Recreational Mathematics & its History, edited by Richard K. Guy and Robert E. Woodrow Lure of the Integers, by Joe Roberts Mathematical Carnival, by Martin Gardner Mathematical Circus, by Martin Gardner Mathematical Cranks, by Underwood Dudley Mathematical Magic Show, by Martin Gardner Mathematics: Queen and Sewant of Science, by E. T. Bell Memorabilia Mathematica, by Robert Edouard Moritz New Mathenutical Diversions, by Martin Gardner Numerical Methods that Work, by Forman Acton Out of the Mouths of Mathematicians, by Rosemary Schmalz Penrose Eles to Trapdoor Ciphers . . . and the Return of Dr. Matrix, by Martin Gardner Polyominoes, by George Martin The Search for E. T. Bell, also known as John Taine, by Constance Reid Shaping Space, edited by Marjorie Senechal and George Fleck Student Research Projects in Calculus, by Marcus Cohen, Edward D. Gaughan, Arthur Knoebel, Douglas S. Kurtz, and David Pengelley The Trisectors, by Underwood Dudley The Words of Mathematics, by Steven Schwartzman MAA Service Center P. 0. Box 91112 Washington, DC 20090-1 112 800-33 1-1MAA FAX 202-206-9789 Prefuce ix 1 CHAPTER Penruse ~bng I 2 CHAPTER Penrose Zbng 11 19 3 CHAPTER MundehoJs fractuh 31 4 CHAPTER Conwa/s Surreul lumbers 49 5 CHAPTER Back fiom the Nondike and Other Problems 63 6 CHAPTER The oulipo 79 7 CHAPTER The Oulipo I/ 95 8 CHAPTER ~ytlro~Ksm 103 9 CHAPTER Pool-Bai7 Triungles und Other Problems 119 10 CHAPTER Muthemutjml Induction und Colored Huts 137 11 CHAPTER Negative Numbers I51 12 c HAPTER Cuffing Shapes into N Congruent Putts 165 13 CHAPTER liopdoor fiphers 183 14 CHAPTER liapdoor fipherr 11 195 15 CHAPTER Hyperbolas 205 16 CHAPTER The New Eleusis 219 17 CHAPTER Ramsey Theory 231 1 8 CHAPTER from Burrs to ~erroca~ 249 19 CHAPTER Sicherman Dice, the Kruskol Count ond Other Curiosities 265 20 CHAPTER Raymond SmuNyannj- logic Puzzles 281 2 1 CHAPTER The Return of Dr. Matuk 293 Postscript 307 Name Index 315 Preface This book is a collection of Scientific American columns that I wrote over a period of 25 years. It is the thirteenth such collection.. The unify- ing theme, if there must be one, is recreational mathematics; that is, mathematics presented in a spirit of play. As with earlier books, the columns have been corrected and expanded with addendums based on current feedback from readers. So much has happened since to Penrose tilings (especially their unexpected applications to crystal theory), to public key cryptosystems and to the French Oulipo, that I have written brand new chapters for each of these topics. Also published lhere for the first time is astonishing news concerning my old and dear friend Dr. Matrix. I report my discovery that Dr. Matrix had not been killed by a Russian KGB agent, as supposed, but is alive and well in Casablanca. Martin Gardner
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