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Questions related to formal languages, grammars, and automata theory

3
votes
Got it. The question makes it seem more complicated than it really is. Let $M$ and $N$ be TMs that recognize $A$ and $B$, respectively. Construct an enumerator $E$ that behaves as follows: For each …
answered Dec 1 '15 by cemulate
2
votes
1answer
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 t …
asked Oct 12 '15 by cemulate
2
votes
2answers
Sorry for long title - the question is a bit unwieldy. To state the question precisely, I'm wondering about the following proposition: Let $\Sigma = \{0,1\}$. If $A$ and $B$ are Turing-recognizabl …
asked Dec 1 '15 by cemulate
5
votes
4answers
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 …
asked Oct 12 '15 by cemulate
4
votes
1answer
Consider the language: $$ L_1 = \{ x \in \Sigma^* : x \text{ does not contain the substring } 110\} $$ I know that there is a DFA that accepts this language, and furthermore, that the regular express …
asked Sep 8 '15 by cemulate
7
votes
1answer
For a language $L$, define: $$ NE(L) = \{x \in L : x \text{ is not the proper prefix of any string in } L\} $$ I'm trying to show context-free languages are not closed under this operation. I've been …
asked Nov 18 '15 by cemulate