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# Class Note for C SC 473 at UA

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Date Created: 02/06/15
CSC 473 Automata Grammars amp Languages Theory of Computation Lecture 02 Preliminaries c sc m Amman cmm e Languages 8222007 Sets mathematics and logic can be constructed One small hierarchy of concepts in this course derives gtG Grammar G V Z R S mg seederee lunction reiatton tnteger tuple set C so we Autumn39s awe Laws Set primitive notion of aggregatequot from which all of rational Sets cont d or false when x is replaced by a particular object PJcxis odd Main predteete ter setwmembership 1 5A Some axioms of set theory AE 1ff VXXEAltXEE L 7 w E 2 w ends in letter 23 Fn 7 n AygtOZgt y C so we Autumn39s awe Laws Predicate Px a statement about a variable x that is true Axtom et Extension 3 set is determined by its extension Axtom et SQecilicalion For every setAand predteete PJc there is eeettx s A 1 Px olallelementsolAlorwhichPistrue EX K 2 x is positive and not prime 46831012 3 X X 15 a string over 3 ab 2 3 A 3x S39Eiy 32 x gt 0 O A x z Lecture 02 CSC 473 Automata Grammars amp Languages Sets cont d Operations and relations on sets A g B subset A c B proper subset A u E union A m B intersection g complement A r B dmerence A Size oi set Special sets empty set W to 1 natural numbers z t 7 271 0 1 2 integers Sets of sets Powerset A x X g A 2 C so on Autumn39s Gamma Laws 8222007 shoot your ambassador S R S RgtS T pay T shot T Fpay Fshot T Fpay T shot T Tpay Fshot F C so on Autumn39s Gamma Laws Logical Implication Material implication R gt S lfyou do not pay us 1 M by midnight R we will Logical Implication cont d shoot your ambassador Q P Q PaQ Tpay Tshot T Fpay Fshot T Fpay Tshot T T pay F shot F C so on Autumn39s Gamma Laws P gt Q If you pay us 1 M by midnight P we will not Lecture 02 CSC 473 Automata Grammars amp Languages 8222007 Quantifiers V Vx for all X 3 3x there exists X Ex defining big Ohquot relationship between functions x 0x2 a SC gt 0 EN gt 0 Vx 2 N fx C x2 Ex continuity of a function at a point epsilondelta defnquot x continuous at C t Vs gt O 35 gt O Vx ix 7 cl lt 5 2 lfx 7 Hal lt s Abe Lincoln39s quote canfoolpt can fool petson p at time t VP at Canfoolp t ABP Vt Canfoolp t A Vp Vt Canfoolp t C so on Autumn Gamma Laws Quantifiers cont d Relationship between V and 3 av 2 3 Ex cannot fool all of the people all of the timequot VP Vt Canfoolpt E 3p 3t canfoolpt Ex noncontinuity at a point Vs gt 165 gt O Vx ix 7 cl lt 5 2 l x r fcl lt s E as gt 0 V5 gt 0 3x ix 7 cl lt 5 A l x r fcl 2 s C so on Autumn Gamma Laws Sets amp Predicates U universe Sets Logical Predicates Px Pom Poo AmB mmBa AuB AJcvBx AB AxVaBx Pz 39 3101300 PU 7 39 VxPx U P P poo xeP Pxtme Pg VxPxQx Po VxPxltQx C so on Amman Gmdbhws 9 Lecture 02 3 CSC 473 Automata Grammars amp Languages 8222007 Tuples 37 unordered pair 2tuple 37 ordered pair 37 E 373 73 2 377 Generalize to ntuple atY a2 a3 an Defn Cartesian Product AXBEab IaEAAbEB Generalization A xAzx x A C so on Autumn39s Gamma Languages Binary Relations Defn a binary relation R from A to B is a subset of A XB R g A X B domain R a e A 3 e B a b e R range R be B Jae Aab R Defn a functionf fromA to B written fA a8 is a relationf gAXB thatis singlevalued ie Vabcab e f ac e f 5 b c Defn onetoone injection onto surjection onetoone correspondence bijection See Delinition 412 p 175 text Also see below C so on Autumn39s Gamma Languages Binary Relations 3 views R g A X B E relation predicate mm W preux m e R m R lb 310 e lt 3 lt 10 lt 310 Ch avleAndvew e Charles ithlthemfAndvew isF thWf ixFatherof Charles Ammw C so on Autumn39s Gamma Languages Lecture 02 4 CSC 473 Automata Grammars amp Languages Ex division with remainder E MMWW ExcircleC g x C X y X2 y Ex Relational Database R Time X Faculty X Room IZUR Time X Room Grammar derives relation E 5 N E 5 E N E 5 E N C so on Nam Gamma Laws Why Relations Generalize Functions Ex functions y X2 lssquareo xl y lssquareof l 0 0 l l 2 4 I 3 9 I EnmqrltgtnmqrA0 rltm Elll0l20l ASE12 i Q l 8222007 Relational Calculus RgAxB 71 R baabER If RAx5saxc then ROSaC3bEBabERAbc C so on Nam Gamma Laws es Relational Inverse RgAxB 39 RIQBXA lt gt Q 2 mef Chzldof Dzvzvaf MulrzpleOf Hzt 1mm i R i R i A B a A C so on Nam Gamma Laws Lecture 02 CSC 473 Automata Grammars amp Languages 8222007 The Calculus IAaaa A 3 Proposition If RAXBSBXCTCgtltD RoSoTRoSoT 7 R o 5quot s o Rquot Rafi R ROIEIA0RR RUSquot Rquotusquot RUSoTRoTUSoT Ro oR c 5cm Aime Gammath 5 Proving a Proposition about Relations Thm R o Squot squot o Rquot Pf a R o squot g squot o Rquot Let Ca R o S Then aC E R o S and 3b 6 B ab e R A bc e S bydefinition of So ma Rquot and ab 6 Squot i a Re and so ca S39 arbitrarilyR 5 Q S b Squot o Rquot g R o Squot Let c a g Squot e RquotThen3b e B b e squot and ba e R39je So bc e S A b e R implying ac e R o 5 Hence a a g R o Squot Since 011 was chosen arbitrarily b follows Slince c a was chosen a R7 c a c 5cm Aime Gammath 7 Relational Properties R gAxB Relational calculus Qredicate calculus name R o R71 Q IA VaElbaRb total dam R A R71 o R IE VabcaRb A aRC singler gt bc valued R e Rquot IA VacbaRb A cRb 171 gt ac injection R71 o R Q IE VbElaaRb onto surjection range R B Pfl Va 6 Ata a E R o R39 ltgt VaaR o R a ltgt Va baRb A bR Ja ltgt Va baRb Pf2 Vbb iaiRquot o Rb gt b b ltgt Vbb VabRquota A aRb gt b b ltgt Vbb WaeRb A aRb gt b b Pf 3 like 2 Pf4 like 1 c 5cm Aime Gammath 5 Lecture 02 6 CSC 473 Automata Grammars amp Languages Family Relationships P XPy E X is Parent of y P 1 isChildol P o P a PP a P2 Grandparent P2Pquot n 2 0 Greatquot Grandparent P lP Sibling Sibling orsef P39lP m f Sibling 71 PP Seller asexualreproductiononly C so on We Gamma Laws PZP 1 Parent Parent 01 child With olispringl 8222007 Family Relationships cont d i P ZP Nephew mece orchild P ij l P 1P2 Uncle Auntor PP 2 Childw oilspring 39 P4192 idoousm Once Removed or P U P2 ParentorGrandparent P U P2 U P3 U Ancestor C so on We Gamma Laws Pingrl P 2P3 lS CouSannce Removed or P E P U P2 U P3 U TransmveclosureolP 2o Binary Relations on A to itself A RgAxA sgAxA RUS ROS AgtltA7R Exny yx1R7lgtlt7V R R lt R3lt R RUR UR3Ur l R R UIlt Thm R R U I C so on We Gamma Laws Lecture 02 CSC 473 Automata Grammars amp Languages 8222007 Properties of R g A X A Name Deln Flelagional Calculus Rrellexive Va 3123 R 3 IA Rsymmetric Vab aRb gt bRa R R l Rtransitive Vabc aRb bRC gtaRC RoRgR R an equivalence relleXive symmetric amp transitive relation c 5cm Nam swabMs 22 A False Proof About Relations Theorem Clearly any symmetric and transitive relation R must be reflexive Pf Assume thatR is symmetric and transitive Then Va b aRb gt bRa By transitivity a Rb bRa gt aRa Since a was chosen arbitrarily it follows that V a aRa D What39swrong sym amp 7 R 9 sym ll main m is true meme argument is correcll c 5cm Nam swabMs 23 RgAxA Digraphs 0 1 Matrices A a b C d Riabbab0cdl a b C d a 0 l 0 0 b l 0 l 0 MR c 0 0 0 l d 0 0 0 0 GR b c d C so on Amman Gmdbhws 2 Lecture 02 8 CSC 473 Automata Grammars amp Languages 8222007 Relations Digraphs Matrices cont d R2aIaaCbbbdl a b C d OOl O OOOH OOl O 0 l 0 l 0 l 0 0 0 0 0 0 OOOH C so on Autumn39s aims Laws Relations Digraphs Matrices cont d R3 labadbab0l 0 1 0 1 3 1 o 1 o 3 Ma MO 0 0 0 0 0 0 0 0 GR3 C so on Autumn39s aims Laws Relations Digraphs Matrices cont d R taaacbbbdi l 0 l 0 0 l 0 1 MR4 MR MR2H 0 0 0 0 l 0 0 0 0 60 Repeats C so on Autumn39s aims Laws Lecture 02 9 CSC 473 Automata Grammars amp Languages RRoR2oR3oR4 l l 0 0 OOHH OOHH OHHH c SC on Autumn swat Laws Relations Digraphs Matrices cont d 8222007 Transitive Closure finite graph c SC on Autumn swat Laws Transitive Closure a Reachability Defn a reachesb in relation digraph R iff 3kgt03aua1 ahauaakb V1O s 1 s k 7 121Ranj Prop a reachesb in Riff aRtb Then RRURQU quotURquot Ex may need to go up to Rquot c SC on Autumn swat Laws Thm LetR A x Abearelation where l A l H Pf Longest possible path in GR that will not repeat an edge is of length n This path will result in an edge in Rquot R R20 O C R3 30 Lecture 02 10 CSC 473 Automata Grammars amp Languages 8222007 Strings and Languages In this course a language is simply a set ofsm39ngsa programming languagequot is much more complex alphabetZ a finite set of symbols String word over 2 M sequence of symbols e the empty or null string 8 i e le length of string w What is a string preclsely7 Stnng w ot length n is a lunction w ln gt Z wj jth symbol String ops X I y Xy concaenaion Xyz XWZ Xs 8X X powers 0 7 11 7 1 w 7 S w 7 w w C so as Autumn smut Laws Strings and Languages cont d 2 w w is a suing over 2 e e 2 Language L over 2 a subsetL 2 Ex 2 la bl L0 25 L1 2 L2 la n prime L3 laa ab ba bbl L4 nab n e W Ex 2ASCcodes Lt blank040 e2 Qii liiu C so as Autumn smut Laws Strings and Languages cont d Language ops Set operatogs 2 L2 g 1 A LtUIutLtoLuLtaIutfmt 7L Concatenation Ll39L2X39yZXELYEL2 Powers L0 S Li L1 39 L EX 2 ab L1 aab L2 bc c L L abcacabbc ExL 22 In E W LL1 lays L3 a U Lglal U Lglsl azn znewlULZlaliiEWl C so as Autumn smut Laws Lecture 02 11 CSC 473 Automata Grammars amp Languages 8222007 Strings and Languages cont d Language ops cont d Dem Kreene erasurersrar Lw3k20 w wlwz wk 3wmWk E L Nore s E L Dem L LL Ex s Ex 2 a b EWaE w w e 2 has at least one a bmebf w w e 2 has exactly one a XYaEWa c SC on Autumn39s Gamma Laws Strings and Languages cont d Theorem E L0 U L1 U L2 U U L1 Pfw e L ltgt 3k 2 03w e L10 Hwk E L w w w lt 3k 2 Ex 2 aim HbHaW s u rbHaf u bua bnaf u b a b a b ref u s u wa Ob Ubw lb Ubw 21 u wa 31 u sUbw0bvlbv2bv3bvm s u b a b c SC on Autumn39s Gamma Laws Strings and Languages cont d ExL a2a3 L s u a2 af Ex Ha bff a by Ex L u a L c SC on Autumn39s Gamma Laws Lecture 02 12 CSC 473 Automata Grammars amp Languages 8222007 Methods of Proof Construction exhibit the object guaranteed by the theorem Ex Construction of a regular expression given a FA Contradiction To show IP Assume P and derive a contraction or clear falsity reduction ad absurdum Ex our proof of undecidability of the halting problem Induction to prove Pn holds for all nonnegative integers n PO base basis Vk Pk e Pk 1 step Vn Pn conclusion lnduc on VD Pn C SC 473 Automata Grammars amp Languages A Rule of Inference PO base Vk Pk a Pk 1 step VD Pn conclusion Prove Pk aPk1 ohalts Vn a1gorithm gt W Pn C SC 473 Automata Grammars amp Languages Lecture 02 13 CSC 473 Automata Grammars amp Languages Kinds of Induction Simple induction Equivalent 1 Pk e 1 gt Pk 1v Ptn CourseofValues Induction PO PM V11 Pm C so on Autumn39s Gamma Laws 8222007 EX Balanced Parentheses are defined inductively by The empty string e is balanced lwls balanced soiww H w kare balanced so is w Nothing else is balanced except by the above rules Remark a grammar for balanced strings is B 4 S B 4 B B 4 BB Exam pl es Baianced 39Unbalamed C so on Autumn39s Gamma Laws Defn The strings having balanced parentheses over Parentheses cont d Ca twisiwhand Cb ny wXy Hixl ZleJ prove 2 directions C so on Autumn39s Gamma Laws Thm A string w is balanced iff it has the prefix property Comment thtsttt cat alogical equivalenceJmeanswe have to l a stnrg is balanced ll hasthe pielix pmpem2 Lemma t below l a stnrg has the pielix ptopetty then ll is balanced e Lemma 2 Defn C A string w over has the prefixproperty C iff Note the prefix property can be checked in a LR scan of the string using a counter this is what calculators do Lecture 02 14 CSC 473 Automata Grammars amp Languages Parentheses contquotd 8222007 c 5cm Autumn swabMs 3 Parentheses cont d Thm A word w is balanced iff it has the prefix property Lemma 1 w balanced 2 w has prefix property C Pf Induction on le Basew0 2 ws gtw satisfies C Step Let lwln Assume IH all strings shorter than n that are balanced satisfy C Let w be balanced Two cases are possible Case wuv where uv are balanced By lH u v satisfy C Then lwlaullvldullvl wl and so w satisfies Ca Next consider a prefix s 0fwuv If s is a prefix of u then because i s l 2 l s l by lH then w satisfies Cb for this prefix c sconAmnmu swabMs Parentheses cont d lfsutwheretisaprefixofvthen l t l 2i t l bylHandso lSllLIlltlli 1lltl ZlUlltllSl and so w satisfies Cb in this case Case w u where u is balanced By IH 4 satisfies C and so clearly so does 14 c 5cm Autumn swabMs 5 Lecture 02 15 CSC 473 Automata Grammars amp Languages C so on Autumn39s aims Laws Parentheses cont d Lemma 2 w satisfies C 2 w is balanced Pf Induction on le Base ws is balanced by definition Step Let lwln gt0 Assume IH all strings shorter than n that satis C are balanced Let w have prefix property C Letx be the shortest prefix of w such thatl X l l X l Such a prefix exits since w has this property Casexw Then w u where 4 satisfies C By lH u is balanced and so then so is w Case xvw with we Nowx satisfies Ca by assumption and satisfies Cb since w does So by lH x is balanced 8222007 C so on Autumn39s aims Laws Parentheses cont d We claim thatvhas propertyC Since l X ll X l andl w ll w l then l V ll V l and so v satisfies Ca Suppose there were a prefix y of v suchthatl y lltl y l Then l XY lltl XY l Which would violate the prefix property of w Thus it must bethatl y l2l y l SovsatisliesCb By lH v is balanced Since both 1 and v are balanced wxv is balanced Lecture 02 16

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