Necessary properties of formal langagues in certain classes that rely on closure against repetition of certain subwords.

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Structure of a Pumping Lemma proof: contradiction or counterexample?

This site is full of Pumping Lemma questions, and I do admit I've not read them all. I've tried some proofs myself and they seem to work, but I can't find anywhere what is the (general) exact ...
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0answers
10 views

Struggling with Pumping Lemma application [duplicate]

I have studied Pumping Lemma carefully and have solved many exercises about it but I can't get an idea on how to solve this one: can anyone help me? Let L = { w#x | x is a substring of w }. Prove ...
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0answers
35 views

Pumping Lemma to prove that L is not context free

I have the language and I want to prove that is not context-free. So I started like this: is variable. Choose w = Case 1: vxy has no c. Choose i = 2 has more a than c or more b than c. Case 2: ...
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1answer
65 views

How to prove {a^(n^2) | n>0} is not context-free?

So I have a language: $$ L = \{a^{n^2} \mid n > 0\} $$ I need to prove that this language isn't context-free using the pumping lemma. I have a vague thought process as to how to do the proof but I'...
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1answer
83 views

Show language is not regular

Show that the following languages are not regular in two ways: first by using closure properties then by using the Pumping lemma: $$\text{(1) L1} = {a^n b^k c^{n+k} : n >= 0; k >= 0}$$ $$\text{...
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3answers
69 views

Proof that whether a regular language is finite is decidable

I have this question for a homework. The question stems from the fact that you can determine whether a regular language is empty by using a Turing machine to count the states n in the given FSM. When ...
0
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1answer
42 views

Prove using pumping free lemma for context-free languages

One of the exercises I tried to make I failed miserably. The question was as follows: Show that the language $L = \{ w \,|\, n_a(w) \cdot n_b(w) = n_c(w) \}$ is not context-free. (with $n_a(w)$ ...
2
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1answer
51 views

How to pick w for the Pumping lemma if the language has no clear pattern?

I'm trying to understanding using the pumping lemma to prove that a language is not regular. I sort of understand how it works when the language describes strings with a particular form, like in this ...
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2answers
54 views

Showing that a language satisfies the pumping lemma

I am wanting to show that this language fails to show that it is not context-free. So, in essence, it satisfies the pumping lemma If L = {ambncndn | m,n >= 1 } Should I have n be the constant of the ...
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0answers
14 views

Proof by pumping lemma [duplicate]

I'm trying to use the pumping lemma proof to show that the following language is context-free rather than regular {ba^n bc^n | n ≥ 1} I've been looking at tutorials on Youtube to try and gain ...
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3answers
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Misconception in taking Pumping Length of language {a} to be $2$

I would like to know why the pumping length of language {a} is $2$ as said in this chat discussion. Eventhough this discussion proves trivially that the pumping length of language {a} is $2$ I ...
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1answer
78 views

Confusion in Pumping Lemma

I would like to know whether we could pump $ba$ into $bbba$ where x=$b$,y=a,z=$\epsilon$ using the finite state machine given in the image 1. For example as given in this image 2 where the string $...
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1answer
35 views

Language where pumping does not work — Pumping lemma [duplicate]

I understand that the length of y must be greater than 0 but I do not understand how to show B_2 is a regular language or why pumping up does not work in part ii.
3
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1answer
63 views

Is no language with the non-primes property context-free?

A language $L$ is said to have the "no primes" property if: For every prime $p$ there are no words $w$ in $L$ s.t. $|w|=p$. For every non-prime $m$ there is at least one word $w\in L$ of length $|w|...
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1answer
66 views

Can $ \{A^nB^nA^nB^n \mid n \geq 0 \}$ be pumped using the pumping lemma?

In order to show that $ \{A^nB^nA^nB^n \mid n \geq 0 \}$ isn't CFL, I was trying to use a pumping lemma this way: At first we assign $w= A^jB^jA^jB^j ,$ $(w^i=uv^ixy^iz), p<|vxy|, p<j.$ if $...
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1answer
154 views

Pumping Lemma for $L = \left \{ a^{c}\mid \text{c is a composite number} \right \}$

$L = \left \{ a^{c}\mid \text{c is a composite number} \right \}$ I feel that this is not a context-free language as checking this constraint requires divisibility checking, but I am facing a hard ...
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1answer
89 views

Showing that $\mathscr{L}$ is not context-free-grammar language

Let $"t"$ and $"s"$ be a words we will say that two words are "completly different" if for all $1\leq i\leq |t|$ the $i$ letter in $t$ diffrent from the $i$ letter in $s$. Prove that the language $...
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1answer
95 views

L=ww is not a CFL

I am studying CFL at the moment and I found this confusing. What I've just read is that, $L=\{ww\}$ is not a CFL. The proof showed it by using pumping lemma for CFL. ($w=0^n1^n0^n1^n$) and I fully ...
1
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1answer
82 views

Show this language is non-regular using pumping lemma: B = {ww | w ∈ {a,b,c,…,z)*} [duplicate]

The question I'm working from is: Prove whether or not a finite automation exists that recognises the following language: B = {ww | w ∈ {a,b,c,...,z)*} EDIT So I believe this is a non-regular ...
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0answers
49 views

Use the pumping lemma to prove that {www} is not context-free

Use the pumping lemma to prove that the following language is not context-free. $\qquad L = \{ w w w \mid w \in \{a,b\}^*\}$ I am studying for an exam and really trying to understand this question. ...
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0answers
39 views

How to prove that the language of words ucv with as many a's in u as b's in v is irregular?

I'm trying to prove that: $L=\{w\in\{a,b,c\}^*\Big|\#_a(u)=\#_b(v),\ \ w=ucv,\ \ \ u,v\in\{a,b\}^*\}$ is irregular, so I'm trying to use the Pumping Lemma. This is what I tried so far: $w=a^ncb^n$...
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1answer
74 views

Language of Palindrome-Prefixed Words

Classify the language $L = \{xx^Rw\ \big|\ (|x| \geq 0\ \wedge |w|\gt 0)\ where\ x,w\in\Sigma^*\}$ as one of: Regular but not Context-Free Context-Free but not Regular Decidable but ...
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2answers
161 views

Pumping lemma: if you can keep pumping, what does this tell you?

Hypothetically, let's say you are using the pumping lemma for either regular or context free languages. Now using either, you come across a case that remains true despite pumping it. In this situation,...
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0answers
10 views

Proving that a language is not regular [duplicate]

Let's say I have a language L where {w^n b^m c^n d^m | where m is greater than or equal to 0, and n is greater than or = to 0 } How can I use the pumping lemma to prove that this is not a regular ...
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1answer
49 views

Why is this language not context free?

I been watching tutorials about how to check if a language is not context-free and in 1 video there was a language: L = {a^n b^n c^n | n ≥ 0} and they used a pumping lemma to prove that it's not ...
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1answer
43 views

How to check if my language is context-free can't seem to solve it using pumping lemma

I have a language and I am trying to see if it's context-free or not, by trying to use a pumping-lemma but I can't figure it out, been reading a lot of other posts but still struggling to apply it to ...
2
votes
1answer
47 views

How to prove that $L_1=1^*\cup \{0^i 1^{j^2}|i\ge 0,j\ge 0\} $ is irregular? [duplicate]

We know that $L=\{0^i 1^{j^2}|i> 0,j\ge 0\} $ is irregular (by the Pumping Lemma), we have to use it to prove two things: $L_1=1^*\cup \{0^i 1^{j^2}|i\ge 0,j\ge 0\} $ is irregular. $L_1$ is ...
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3answers
55 views

Why does it seem as if I can apply the Pumping lemma to a language that is regular?

We learn about the Pumping Lemma at the class and I tried to make few examples to understand it... There I make this example: Let's say: $L=\{w\in L|w=(0+1)^*1\}$ - i.e. - L is the language of all ...
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1answer
530 views

What is the minimum pumping length of the following languages?

How to determine the minimum pumping length of union of two languages? How do I proceed after determining the individual pumping lengths? 0*1+0+1* U 10*1 - Here the minimum pumping length of the ...
3
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1answer
245 views

Is {ww^r ww^r} a context-free language?

Is the language $L = \{w w^r w w^r \mid w \in \Sigma^*\}$ context-free? ($w^r$ is the reversal of $w$.) I heard that by using the pumping lemma, we can only prove that a language is not context-free, ...
2
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1answer
48 views

If a language has any single occurrence of a letter, is it not context-free?

From what I understand, the rules for CFL from my notes say: If $L$ is a language and • for all integers $N$, • there is a string $w \in L$ of length greater than $N$ such that • for all ways of ...
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2answers
125 views

Using closure properties to show that $a^n b^m a^{n+m}$ is not regular

I want to show that $L = \{a^n b^m a^{n+m} \mid n, m \geq 0\}$ is not regular. Can I say that the complement of $L$ intersected with $a^*b^*$ equals $\{a^n b^n \mid n \geq 0\}$ and since I know that $...
2
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3answers
109 views

Proof that a given language is not context-free

Given the language $L = \{w \in \{a,b\}^* \, | \, |w| = n \cdot \sqrt{n} \text{ and } n \geq 42\}$ and the assignement to proof that $L \notin CFL$ with the Pumping lemma. Assuming $L \in CFL$, ...
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4answers
223 views

Proving non-regularity of $u u^R v$?

This particular language: $$L = \{ u u^R v \,:\, u, v \in \{0, 1\}^+\}$$ is giving me a lot of trouble. I highly suspect that its non-regular, considering that $\{ u u^R : u \in \{0, 1\}^+\}$ is non-...
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0answers
28 views

Can somebody please explain what the pumping lemma is? [duplicate]

I've had multiple lectures on the pumping lemma but still can't grasp exactly what it is...my main questions are as follows What is the pumping lemma for? How do you use it to prove a language is ...
2
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1answer
32 views

'Quick' way to show non-regularity of languages that are 'close' to other non-regular langauges

Take the language $L = \{a b^n c^n \; : \; n \geq 0\}$. It's obvious that $L$ is non-regular because $\{b^n c^n \; : \; n \geq 0\}$ is non-regular, but I don't know a satisfying way to show that to ...
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1answer
50 views

Pumping lemma regular language can't be pumped

Suppose we have a regular language that describes every string with the exact length of 3.That is obviously a regular language and it still can't be pumped because there is no cyclic behavior in that ...
5
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1answer
212 views

What's wrong with my pumping lemma proof?

The language $L = \{0^{2n} \space |\space n \ge 0 \}$ is obviously regular – for example, it matches the regular expression $(00)^*$. But the following pumping lemma argument seems to show it's ...
2
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1answer
152 views

Showing that the pumping lemma cannot prove that some language is not regular

I have this language $ L = a^* \cup \left \{ a^mb^n|m>n\geq 0 \right \}^* $ I have to prove that this language is not regular but still satisfies the pumping lemma for regular languages (Since the ...
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1answer
72 views

Proving that if $L=\{ a^n b^n c^n \colon n\ge 0 \}$ than $L\notin CFL$ [closed]

I'm going over "Introduction to the Theory of Computation" by Michael Sipser in which there's an example of using the pumping lemma for CFLs to prove that $L=\{ a^n b^n c^n \colon n\ge 0 \}$ is not a ...
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1answer
162 views

Does every language that fulfills the regular Pumping conditions also fulfill the context-free ones?

Let L be a language that fulfills the properties implies by the Pumping lemma for regular languages. Does L necessarily fulfill the corresponding properties of the Pumping lemma for context-free ...
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84 views

The pumping lemma - Proving that this language is NOT context free [duplicate]

I would like to find out if this language is context free or not: $\qquad L=\{a^{i}b^{j}c^{k} \mid i<j,i+2j+3<k\}$. I've tried to apply the pumping lemma taking out $w=a^n b^{n+1}c^{3n+6}$ ...
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1answer
122 views

Using the pumping lemma to prove that a language is context-free [duplicate]

I am new to automata theory. Could you give me a little hand with the correct use of the pumping lemma? I understand now how to proof a language is not context-free, but how do I use the pumping ...
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1answer
152 views

How to prove that the language { ww | w ∈ {a,b}* } is / isn't context free? [duplicate]

Is the language { ww | w ∈ {a,b}* } context free? I have tried to create a pushdown automaton but I didn't find any solution. I think you need a queue and not a stack. Is there a way to prove this ...
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1answer
123 views

Is the language $L=\{a^{2^{n}} \mid$ n is a natural number$\} $ context free?

I have to determine, and prove, whether the language $L=\{a^{2^{n}} \mid$ n is a natural number$\}$ is context free or not (if it is by a grammar and not by the pumping lemma). I tried to construct ...
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1answer
52 views

Irregularity of L = {a^i b^(j+3)| i!=j }

I have a question to find out that $L = \{a^i b^{j+3}\mid i\ne j \}$ is regular or not. I know that it is not regular. I tried with pumping lemma but I am finding just a specific number of $v$'s in $u ...
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1answer
49 views

Use the pumping lemma to show that the language is not regular [closed]

I am working on this problem : Use the pumping lemma to show that the language $\{0^n 1^{n} \mid n ≥ 1\}$ is not regular. May someone give me some suggestion about how to solve this problem?
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1answer
136 views

Proving a language isn't regular using the pumping lemma [closed]

Let the language $$ L = \{ a^nb^m : m,n \text{ has the same integer-quotient, (ignoring the remainder) } \} $$ Show that $L$ isn't regular using the pumping-lemma. Let's assume by contradiction ...
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1answer
82 views

Proof that a language is not regular using pumping lemma

I have a language $L$ that I think is not regular: $L = \{w\in \{0,1,...,9\}^* \; | \enspace w \enspace \text{is a decimal representation of a number divisible by 3}\}$ I'm using pumping lemma in my ...
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0answers
30 views

Ogden’s lemma on CFG

I'm trying to understand Ogden's lemma, and I know there are 4 cases, but in the next example I can only find 3: Assume A = {$0^n1^m0^k$ | k = $max${n, m}} is CF: Choose z = $0^k1^k0^k ∈ A$, z = ...