152 questions linked to/from How to prove that a language is not regular?
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Is this language regular or non-regular: {ww : w ∈ {a,b}* } [duplicate]

This is a question from a text book that's giving me some trouble. The question is: Determine whether or not this language is regular. Justify your answer. $$L = \{ww : w \in \{a,b\}^* \}$$ I ...
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Proof that {$a^m b^n$ | m!=n} is not regular [duplicate]

I know that the language $\{a^m b^n | n\neq m\}$ satisfies the pumping lemma, but it's still not regular (I have to count the # of a's and b's). How can I formally prove it?
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Show that a language consisting of strings of a prime number of 1s is irregular using pumping lemma [duplicate]

Question: L is a language defined as $\ L = \{1^l | l\in primes\}$ (strings of 1s having a prime length). Show that this is not a regular language ($\ L \notin REG$). You may either use the theory ...
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Proving that {0^{2^k}} is not regular with the Myhill-Nerode theorem [duplicate]

My language is the repetition of 0 to a length that's a power of 2: $L = \{ 0^k \ni k=2^n, n \geq 1 \}$ I want to know how to prove that this language is not regular. I have attempted the proof ...
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Union of finite and non-regular language [duplicate]

Question: ($B$ and $C$ are languages) $B$ is finite,$C$ isn't regular: Prove/Disprove: $C\cup B$ isn't regular. Thoughts: My intuition says this is true, but I need an idea to prove it. Since I don'...
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Prove that the language L = {a^(m+n) b^m a^n | m, n ≥ 0} ∪ {a^m b^n a^(m+n) | m, n ≥ 0} is not regular [duplicate]

In general, how can we go about proving that union of two languages as non regular. In this case, the individual languages can be proved as non regular using pumping lemma. How can we apply pumping ...
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Class of a Language [duplicate]

What are the common ways to check if a given language is regular, context free, or context sensitive? Any surveys or notes would also be helpful. There's no need to describe your suggestions. eg. it ...
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Proving a language is regular or non-regular [duplicate]

I'm struggling a bit to understand two of the problems we were given in class. Could someone look over my work and maybe give me a few hints? State whether the following languages are regular or not ...
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Prove EXP to be regular or non-regular [duplicate]

Given L is regular, Prove/Disprove that the following language is regular or not. $EXP = \{w| w^{|w|} ∈L\}$
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Proving that language is regular or not [duplicate]

How to prove that the language over the alphabet $\{0, 1, +, =\}$ is regular or not: $\{a+b=c:a,b,c \text{ are integers in binary for which } a \text{ plus } b\text{ equals } c\}$ I started with the ...
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Show that a language is not regular using the Pumping Lemma [duplicate]

Possible Duplicate: How to prove that a language is not regular? Given a language $L = \{a^pb^{2p} \mid p \ge 1\}$, how could I show, using the Pumping Lemma that $L$ is not regular?
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Can't tell whether the following language is regular or not: [duplicate]

I have to decide if the following language is regular or not. I suspect it is not regular, so I try using pumping lemma to prove it, but something goes wrong. Any help on how to use pumping lemma on ...
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If there is comparison between two variables then language is not regular. Then how the below two languages L1 and L2 Regular? Please Explain [duplicate]

How these two languages be regular.If there is comparison between m and n since (n < m) is the condition to be satisfied.
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Show that a language is not regular by Pumping Lemma [duplicate]

Possible Duplicate: How to prove that a language is not regular? Show that $L_2=\{a^nb^k|n\not= k-1\}$ is not regular by Pumping Lemma.
Proving that $\{0^nw1^n\mid n\geq 0, w\in\{0,1\}\}$ is irregular [duplicate]
How can I prove that the language $L = \{0^nw1^n\mid n\geq0,w\in\{0,1\}\}$ is irregular? I've tried the pumping lemma but that seems not to work.