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Results tagged with formal-languages
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user 54078
Questions related to formal languages, grammars, and automata theory
4
votes
Accepted
Classes of languages for which the language $\{a_1^n \cdots a_k^n \mid n \geq 0\}$ is in the...
One example would be the hierarchy defined by blind counter automata.
A blind $k$-counter automaton has access to $k$ counters for which
there is an increment and a decrement instruction (and no zer …
- 361
4
votes
regular expression of star-height 1
The language has star-height 2. Note that the language includes
$R_0=(ba^+ba^+)^*$, but is disjoint from $R_1=(ba^+ba^+)^*ba^+$. Therefore, it suffices to show:
Claim: If $L$ has star-height 1 and $R …
- 361
2
votes
Regular expressions and semi-linear sets
The claim fails for two symbols. The Parikh image $M\subseteq \mathbb{N}\times\mathbb{N}$ of $(abb^*)^*$ is not linear:
It is easy to see that for every finitely generated submonoid $N$ of $M$, there …
- 361
8
votes
Accepted
Can there be a context-sensitive pumping lemma?
Here is some evidence that there is no pumping lemma for the context-sensitive
languages.
Of course, an answer hinges on the question what constitutes a pumping
lemma. The weakest reasonable definit …
- 361