CS2303 TOC 2 MARKS.pdf

States input 0 1 q0 q1 q0 q1 q2 q2 q q 1 q 2 0 1 1 0

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States Input 0 1 {q0} {q1} {q0} {q1} - {q2} {q2} - - q 0 q 1 q 2 0 1 1 0 1 q 2

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III Year V Semester CSE CS2303 Theory of Computation Adhiparasakthi College of Engg., G.B. Nagar, Kalavai Page 8 of 20 Unit - II 1. State regular expression. Let Σ be an alphabet. The regular expressions over Σ and the sets that they denote are defined recursively as follows a. Ø is a regular expression and denotes the empty set. b. is a regular expression and denotes the set { } c. For each a Σ, ‘a’ is a regular expression and denotes the set {a}. d. If ‘r’ and ‘s’ are regu lar expressions denoting the languages L 1 and L 2 respectively then r + s is equivalent to L 1 U L 2 i.e. union rs is equivalent to L 1 L 2 i.e. concatenation r * is equivalent to L 1 * i.e. closure 2. How the kleen ’s closure or closure of L can be denoted? n L * = U L i (e.g. a * ={ ,a,aa,aaa,……}) i=0 3. How do you represent positive closure of L? n L + = U L i (e.g. a + ={a,aa,aaa,……}) i=1 4. Write the regular expression for the language accepting all combin ations of a’s over the set = {a}. L = { a,aa,aaa,………………….} R= a * (i.e. kleen closure) 5. Write regular expression for the language accepting the strings which are starting with 1 and ending with 0, over the set = {0,1}. L = { 10,1100,1010,100010………………….} R= 1(0+1) * 0 6. Show that (0*1*)* = (0+1)*. LHS : (0*1*)* = { , 0,1,00,11,0011,011,0011110……………….} RHS : (0+1)* = { , 0,1,00,11,0011,011,0011110……………….} Hence LHS = RHS is proved 7. Show that (r+s)* r* + s*. LHS : (r+s)* = { , r,s,rs,rr,ss,rrrsssr,……………….} RHS : r* + s* = { , r,rr,rrr………….}U { , s,ss,sss,………….} = { , r,rr,rrr,s,ss,ssss……………..} Hence LHS ≠ RHS is proved
III Year V Semester CSE CS2303 Theory of Computation Adhiparasakthi College of Engg., G.B. Nagar, Kalavai Page 9 of 20 8. What do you mean by homomorphism? A string homomorphism is a function on strings that works by substring a particular sting for each symbol. Eg. h(0) = ab h(1) = is a homomorphism, where replace all 0’s by ab and replace all 1’s by . Let w = 0011 h(w) = abab 9. Explain the application of the pumping lemma. Pumping Lemma is used to prove the language is not regular. 10. Describe the following by regular expression a. L1 = the set of all strings of 0’s and 1’s ending in 00. b. L2 = the set of all strings of 0’s and 1’s beginning with 0 and ending with 1. r1 = (0+1)*00 r2 = 0(0+1)*1 11. Show that (r*)* = r* for a regular expression r. LHS = r* = { ε, r,rr,rrr, …………….) (r*)* = { ε, r,rr,rrr, …………….)* (r*)* = { ε, r,rr,rrr, …………….) = r* LHS = RHS 12. Write down the closure properties of regular language. The regular languages are closed under 1. Union 2. Intersection 3. Complement 4. Difference 5. Reversal 6. Closure 7. Concatenation 8. Homomorphism 9. Inverse Homomorphism 13. Write down the relationship between FA and regular expression.

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