`- AUTOMATA THEORY,
`LANGUAGES,
`COMPUTATION
`
`AND
`
`JOHN E. HOPCROFT
`
`JEFFREY D. ULLMAN
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`EXPERIAN EXHIBIT 1011
`IPR2023-01406
`
`EXPERIAN EXHIBIT 1011
`IPR2023-01406
`
`
`
`
`
`
`
`LANGUAGES,
`COMPUTATION
`
`AND
`
`JOHN E. HOPCROFT
`Cornell University
`
`JEFFREY D. ULLMAN
`Princeton University
`
`A
`vv
`
`SLEY PUBLISHING COMPANY
`ADDISON-WE
`Menlo Park, California
`Reading, Massachusetts *
`Ontario + Sydney
`London + Amsterdam ° Don Mills,
`
`
`
`
`
`
`
`
`Hoperoft, JohnE.,
`
`
`
`
`
`
`
`
`
` juages, and
`
`computation.
`
`
`
`Copyright © 1979 by
`Addison-Wesley Publishing Company, Inc.
`Philippines copyright 1979 by
`Addison-Wesley Publishing Company,Inc.
`All rights reserved. No part of this publication may
`be reproduced,stored in a retrieval system, or
`transmitted, in any form or by any means,
`sictronic, mechanical, photocdpying, recording, oF
`otherwise, without the prior written permission of
`the publisher. Printed in the United States of
`Amer1a. Published simultaneously in Canada.
`Library of Congress Catalog Card No. 78-67950.
`ISBN: 0-201-02988-x
`ST-DO-943210
`
`Library of CongressCatalogingin Publica fon
`
`
`
`
`Bibliography: Pp.
`
`Includes index. .
`oh
`
`
`1. Machine
`theory.
`
`
`3. Computational
`Jeffrey D., 1942-
`Qn267.456.°
` 629.81512
`
`
`ISBN 0-201-02988-x
`
`
`
`
`
`CHAPTER
`
`
`
`PRELIMINARIES
`
`In this chapter we survey the principal mathematical ideas necessary for under-
`standing the material in this book. These concepts include graphs,trees, sets,
`relations, strings, abstract languages, and mathematical induction. Wealso pro-
`vide a brief introduction to, and motivationfor, the entire work. The reader with a
`background in the mathematical subjects mentioned can skip to Section 1.6 for
`motivational remarks.
`
`1.1 STRINGS, ALPHABETS, AND LANGUAGES
`
`A “symbol”is an abstract entity that we shall not define formally, just as “point”
`and “line” are not defined in geometry. Letters and digits are examples of
`frequently used symbols. A string (or word) is oliReavence of symbols jux-
`taposed. For example, a, b, and c are symbols and abc isa string. The length ofa
`string w, denoted |w/|, is the number of symbols composingthestring. For exam-
`ple, abcb has length 4. The emptystring, denoted by ¢,is the string consisting of
`zero symbols. Thus |¢| = 0.
`:
`:
`A prefix of a string is any numberofleading symbols of that string, and a
`suffix is any numberoftrailing symbols. For example,string abc has prefixes€,
`a, ab,
`and abe:its suffixes are ¢, c, bc, and abc. A prefix or suffix of a string, other than the
`_
`String
`itself, is called a proper
`prefix or suffix.
`8
`oO
`The concate tion‘of cae is the string formed by writing the first,
`
`lo
`d, with no intervening space. For example, the concatena-
`
`ise
`is doghouse. Juxtaposition is used as the concatenation
`
`and x arestrings, then wx is the concatenation of these two
`
`
`
`