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Peter Linz Edition 4 Exercise 8.1 Question 8 (Page No. 212)
Determine whether or not the following languages are context-free. (a) $L=$ {$a^nww^Ra^n : n ≥ 0, w ∈$ {$a,b$}*} (b) $L=$ {$a^nb^ja^nb^j : n ≥ 0, j ≥ 0$}. (C) $L=$ {$a^nb^ja^jb^n : n ≥ 0, j ≥ 0$}. (d) $L=$ {$a^nb^ja^kb^l : n + j ≤ k + l$ ... $ L=$ {$a^nb^nc^j : n ≤j$}. (g) $L=$ {$w ∈$ {$a, b, c$}* $: n_a(w)= n_b (w)=2n_c(w)$}.

asked Jun 25 in Theory of Computation by Naveen Kumar 3 Boss (14k points) | 51 views

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Michael Sipser Edition 3 Exercise 2 Question 36 (Page No. 158)
Give an example of a language that is not context free but that acts like a $CFL$ in the pumping lemma$.$ Prove that your example works$.$ $\text{(See the analogous example for regular languages in Question 54.)}$

asked May 4 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 47 views

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Michael Sipser Edition 3 Exercise 2 Question 35 (Page No. 157)
Let $G$ be a $CFG$ in Chomsky normal form that contains $b$ variables$.$ Show that if $G$ generates some string with a derivation having at least $2^{b}$ steps$, L(G)$ is infinite$.$

asked May 4 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 26 views

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Michael Sipser Edition 3 Exercise 2 Question 34 (Page No. 157)
Let $G = (V, \Sigma, R, S)$ be the following grammar. $V = \{S, T, U\}; \Sigma = \{0, \#\};$ and $R$ is the set of rules$:$ $S\rightarrow TT\mid U$ $T\rightarrow 0T\mid T0\mid \#$ ... existence of a pumping length $p$ for $B.$ What is the minimum value of $p$ that works in the pumping lemma$?$ Justify your answer$.$

asked May 4 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 56 views

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Michael Sipser Edition 3 Exercise 2 Question 32 (Page No. 157)
Let $\Sigma = \{1, 2, 3, 4\}$ and $C = \{w\in\Sigma^{*}\mid$ $\text{in $w$, the number of $1's$ equals the number of $2's,$ and the number of $3's$ equals the number of }$4's\}.$ Show that $C$ is not context free$.$

asked May 4 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 40 views

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Michael Sipser Edition 3 Exercise 2 Question 26 (Page No. 157)
Show that if $G$ is a $CFG$ in Chomsky normal form$,$ then for any string $w\in L(G)$ of length $n\geq 1,$ exactly $2n − 1$ steps are required for any derivation of $w.$

asked May 4 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 23 views

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Michael Sipser Edition 3 Exercise 2 Question 25 (Page No. 157)
For any language $A,$ let $SUFFIX(A) = \{v\mid uv \in A$ $\text{for some string u\}}.$ Show that the class of context-free languages is closed under the $\text{SUFFIX operation.}$

asked May 4 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 19 views

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Michael Sipser Edition 3 Exercise 2 Question 24 (Page No. 157)
Let $E=\{a^{i}b^{j}\mid i\neq j$ $\text{and}$ $2i\neq j\}.$ Show that $E$ is a context-free language$.$

asked May 4 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 19 views

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Michael Sipser Edition 3 Exercise 2 Question 23 (Page No. 157)
Let $D = \{xy\mid x, y\in \{0,1\}^{*}$ $\text{and}$ $\mid x\mid = \mid y\mid$ $\text{but}$ $x\neq y\}.$ Show that $D$ is a context-free language$.$

asked May 4 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 20 views

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Michael Sipser Edition 3 Exercise 1 Question 73 (Page No. 93)
Let $\sum = \{0,1, \#\}.$ Let $C = \{x\#x^{R}\#x| x\in\{0,1\}^{*}\}.$Show that $\overline{C}$ is a $\text{CFL}.$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 14 views

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Michael Sipser Edition 3 Exercise 1 Question 72 (Page No. 93)
Let $M_{1}$ and $M_{2}$ be $\text{DFA's}$ that have $k_{1}$ and $k_{2}$ states, respectively, and then let $U = L(M_{1})\cup L(M_{2}).$ Show that if $U\neq\phi$ then $U$ contains some string $s,$ where $|s| < max(k1, k2).$ Show that if $U\neq\sum^{*},$ then $U$ excludes some string $s,$ where $|s| < k1k2.$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 41 views

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Michael Sipser Edition 3 Exercise 1 Question 71 (Page No. 93)
Let $\sum = \{0,1\}$ Let $A=\{0^{k}u0^{k}|k\geq 1$ $\text{and}$ $u\in \sum^{*}\}.$ Show that $A$ is regular. Let $B=\{0^{k}1u0^{k}|k\geq 1$ $\text{and}$ $u\in \sum^{*}\}.$Show that $B$ is not regular.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 19 views

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Michael Sipser Edition 3 Exercise 1 Question 70 (Page No. 93)
We define the $\text{avoids}$ operation for languages $A$ and $B$ to be $\text{A avoids B = {w| w ∈ A and w doesn’t contain any string in B as a substring}.}$ Prove that the class of regular languages is closed under the ${avoids}$ operation.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 12 views

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Michael Sipser Edition 3 Exercise 1 Question 69 (Page No. 93)
Let $\sum=\{0,1\}.$ Let $WW_{k}=\{ww|w\in \sum^{*}$ and $w$ is of length $k\}.$ Show that for each $k,$ no DFA can recognize $WW_{k}$ with fewer than $2^{k}$ states. Describe a much smaller $NFA$ for $\overline{WW_{k}},$ the complement of $WW_{k}.$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 15 views

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Michael Sipser Edition 3 Exercise 1 Question 68 (Page No. 93)
In the traditional method for cutting a deck of playing cards, the deck is arbitrarily split two parts, which are exchanged beforereassembling the deck. In a more complex cut, called $\text{Scarne's cut,}$ the deck is broken into three parts ... $ CUT(CUT(B)).}$ Show that the class of regular languages is closed under $\text{CUT}.$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 32 views

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Michael Sipser Edition 3 Exercise 1 Question 61 (Page No. 92)
Let $Σ = \{a, b\}.$ For each $k\geq 1,$ let $C_{k}$ be the language consisting of all strings that contain an a exactly $k$ places from the right-hand end$.$ Thus $C_{k}=\sum^{*}a\sum^{k-1}.$ Prove that for each $k,$ $\text{no DFA}$ can recognize $C_{k}$ with fewer than $2^{k}$ states.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 8 views

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Michael Sipser Edition 3 Exercise 1 Question 58 (Page No. 92)
If $A$ is any language,let $A_{\frac{1}{2}-\frac{1}{3}}$ be the set of all strings in $A$ with their ,middle thirds removed so that $A_{\frac{1}{2}-\frac{1}{3}}=\{\text{xz|for some y,|x|=|y|=|z| and xyz $\in$ A\}}.$ Show that if $A$ is regular,then $A_{\frac{1}{2}-\frac{1}{3}}$ is not necessarily regular.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 5 views

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Michael Sipser Edition 3 Exercise 1 Question 57 (Page No. 92)
If $A$ is any language,let $A_{\frac{1}{2}-}$ be the set of all first halves of strings in $A$ so that $A_{\frac{1}{2}-}=\{\text{x|for some y,|x|=|y| and xy $\in$ A\}}.$ Show that if $A$ is regular,then so is $A_{\frac{1}{2}-}.$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 15 views

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Michael Sipser Edition 3 Exercise 1 Question 56 (Page No. 91)
If $A$ is a set of natural numbers and $k$ is a natural number greater than $1,$ let $B_{k}(A)=\{\text{w| w is the representation in base k of some number in A\}}.$ Here, we do not allow leading $0's$ in the representation of a ... a set $A$ for which $B_{2}(A)$ is regular but $B_{3}(A)$ is not regular$.$ Prove that your example works.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 25 views

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Michael Sipser Edition 3 Exercise 1 Question 55 (Page No. 91)
The pumping lemma says that every regular language has a pumping length $p,$ such that every string in the language can be pumped if it has length $p$ or more. If $p$ is a pumping length for language $A,$ so is any length $p^{'}\geq p.$ The minimum pumping ... $\epsilon$ $1^{*}01^{*}01^{*}$ $10(11^{*}0)^{*}0$ $1011$ $\sum^{*}$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 20 views

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Michael Sipser Edition 3 Exercise 1 Question 54 (Page No. 91)
Consider the language $F=\{a^{i}b^{j}c^{k}|i,j,k\geq 0$ $\text{and if}$ $ i = 1$ $\text{then} $ $ j=k\}.$ Show that $F$ is not regular. Show that $F$ acts like a regular language in the pumping lemma. ... three conditions of the pumping lemma for this value of $p.$ Explain why parts $(a)$ and $(b)$ do not contradict the pumping lemma.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 27 views

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Michael Sipser Edition 3 Exercise 1 Question 53 (Page No. 91)
Let $\sum=\{0,1,+,=\}$ and $ADD=\{x=y+z|x,y,z$ $\text{are binary integers,and}$ $x$ $\text{is the sum of}$ $y$ $\text{and}$ $z\}.$ Show that $\text{ADD}$ is not a regular.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 8 views

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Michael Sipser Edition 3 Exercise 1 Question 52 (Page No. 91)
$\text{Myhill-Nerode theorem.}$ Refer to $\text{Question 51}.$Let $L$ be a language and let $X$ be a set of strings. Say that $X$ is $\text{pairwise distinguishable}$ by $L$ if every two distinct strings in $X$ are ... $\text{DFA}$ recognizing it$.$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 10 views

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Michael Sipser Edition 3 Exercise 1 Question 51 (Page No. 90)
Let $x$ and $y$ be strings and let $L$ be any language. We say that $x$ and $y$ are $\text{distinguishable}$ by $L$ if some string $z$ exists whereby exactly one of the strings $xz$ and $yz$ ... $≡L$ is an equivalence relation. A $\text{palindrome}$ is a string that reads the same forward and backward.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 6 views

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Michael Sipser Edition 3 Exercise 1 Question 50 (Page No. 90)
Read the informal definition of the finite state transducer given in Question $24.$ Prove that $\text{no FST}$ can output $w^{R}$ for every input $w$ if the input and output alphabets are $\{0,1\}.$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 6 views

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Michael Sipser Edition 3 Exercise 1 Question 49 (Page No. 90)
Let $B=\{1^{k}y|y\in\{0,1\}^{*}$ $\text{ and y contains at least}$ $k$ $1's,$ $\text{for every}$ $k\geq 1\}.$ Show that $B$ is a regular language. Let $C=\{1^{k}y|y\in\{0,1\}^{*}$ $\text{ and y contains at most}$ $k$ $1's,$ $\text{for every}$ $k\geq 1\}.$ Show that $C$ isn’t a regular language.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 20 views

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Michael Sipser Edition 3 Exercise 1 Question 48 (Page No. 90)
Let $\sum = \{0,1\}$ and let $D = \{w|w$ $\text{contains an equal number of occurrences of the sub strings 01 and 10}\}.$ Thus $101\in D$ because $101$ contains a single $01$ and a single $10,$ but $1010\notin D$ because $1010$ contains two $10's$ and one $01.$ Show that $D$ is a regular language.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 5 views

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Michael Sipser Edition 3 Exercise 1 Question 47 (Page No. 90)
Let $\sum=\{1,\#\}$ and let $Y=\{w|w=x_{1}\#x_{2}\#...\#x_{k}$ $\text{for}$ $k\geq 0,$ $\text{each}$ $ x_{i}\in 1^{*},$ $\text{and}$ $x_{i}\neq x_{j}$ $\text{for}$ $i\neq j\}.$ Prove that $Y$ is not regular.

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 7 views

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Michael Sipser Edition 3 Exercise 1 Question 46 (Page No. 90)
Prove that the following languages are not regular. You may use the pumping lemma and the closure of the class of regular languages under union, intersection,and complement. $\{0^{n}1^{m}0^{n}|m,n\geq 0\}$ $\{0^{m}1^{n}|m\neq n\}$ $\{w|w\in\{0,1\}^{*} \text{is not a palindrome}\}$ $\{wtw|w,t\in\{0,1\}^{+}\}$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 10 views

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Michael Sipser Edition 3 Exercise 1 Question 43 (Page No. 90)
Let $A$ be any language. Define $\text{DROP-OUT(A)}$ to be the language containing all strings that can be obtained by removing one symbol from a string in $A.$ Thus, $\text{DROP-OUT(A) = $\{xz| xyz\in A$ where $x, ... $\text{Theorem 1.47.}$

asked Apr 30 in Theory of Computation by Lakshman Patel RJIT Boss (45.8k points) | 10 views

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