Linked Questions

Is there an algorithm/systematic procedure to test whether a language is context-free? In other words, given a language specified in algebraic form (think of something like $L=\{a^n b^n a^n : n \in \...

We learned about the class of regular languages $\mathrm{REG}$. It is characterised by any one concept among regular expressions, finite automata and left-linear grammars, so it is easy to show that a ...

How I use the pumping lemma to prove that the language $L = \{ a^{j!} \mid j \geq1\}$ is not context-free?

Let $ACFG$ be the language of all encodings $(C,x)$ where $C$ is a context free grammar that generates a language containing $x$, i.e. $ACFG$ is the acceptance problem for context free grammars. It ...

When I prove some language is context free, It is too hard to find example string. Is there any tips? It takes too many time or eventually give up.

I'm trying to prove that that language isn't a context free: $ L = \{ w11w \mid w\in \Sigma^* = \{0,1\}\}$ I succeed to prove that $L = ww$ isn't context free, but not the language above. What ...

Could I get help to prove that the language $\{a^i b^j c^k \mid i>j>k\ge 0\}$ is not context free language by using pumping lemma?

Is anybody can help me please to determine is this language is Context-free language or not? L={wvw | w,v∈{a,b,c}+} for example: part of the language: acbac, abcab, bbcbb not part of the language:...

Let L = { uv composed of {0,1} | |u| = |v| and u = v } Do we agree that this language is not a Context Free Language ? If not, why ? Can you give me a pushdown automata that recognizes it or the ...

It is known that in the case of a Regular Language $L$ , the pumping lemma can be extended to apply to any sufficiently long subword of the language, ie, if $uwv \in L$ and $|w| \ge p$ then we can ...

$L = \{x \in(a,b,c,d)^* \mid -10 \leq ( |x|_a + |x|_b) - ( |x|_c + |x|_d) \leq 10 \}$ I don't have any idea. Can someone help me.

$ L = \{ww^{R} \in \{a, b\}^{*} : |w|_{a} \equiv |w|_{b} \equiv 0$ $ (mod$ $13) \} $ Exercises: If the language L is regular (build a DFA or regular expression) else if the language L is context-...

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,...

Is this language context-free? $\Sigma$ = {a,b,#}, L = {x1#x2#...#xk : k$\geq$2, every $x_i \in$ {a,b}* and xi $\neq$ xj for every pair i $\neq$ j} I think it is not, because the PDA can't memorize ...

Been trying to figure it out for an hour myself and another hour looking around, I cannot find anything with the $c^{mn}$ part. $$L=\{a^mb^nc^{mn}\mid m>n\}$$