Questions tagged [regular-language]
Questions about the formal languages that can be described by regular expressions (in the sense of Kleene), or, equivalently, the languages that can be accepted by finite automata.
135
questions
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Updating (minimal) DFA incrementally
Is there algorithm to incrementally update (minimal) DFA? Namely, having relatively large minimized DFA I want to update it incrementally using union and sudtraction with other (relatively small, ...
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votes
0
answers
62
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How to reduce a code down to its configuration
I have built a system where from atomic information of a UI code I could generate a framework specific code. Here is the concept https://github.com/imvetri/ui-editor. For example, the user of this ...
- 99
7
votes
1
answer
151
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Complexity of the inevitability problem over monoids
I am interested in the complexity of following problem:
Inevitability problem in monoids
Input: two regular languages $K$, $L$ specified by finite monoids $M_K$ and $M_L$ (+ morphisms and accepting ...
- 143
7
votes
1
answer
333
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Converting 2-ambiguous NFA to unambiguous NFA
This must be known, but somehow I can't locate a reference about this. Let $A$ be a nondeterministic finite automaton (NFA) over words of an alphabet $\Sigma$. I say that $A$ is unambigous if, for ...
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0
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Overlap operator for simple ( regex-like ) Patterns
( Introduction )
Some Notation
lower case letters, $a, b, c$ will be used to denote single symbols
Upper case letters, $P, Q, R$ will be used to denote string of symbols
$a\!:\!S$ means a string ...
- 11
2
votes
0
answers
72
views
Languages free of concatenations of stars
Union-free regular languages, defined by regular expressions (using $*$, literals (alphabet symbols), and concatenation) excluding union (written $+$ or $\cup$) have been studied.
Note that unions ...
- 4,475
3
votes
1
answer
137
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What is the solution of this equation on regular languages?
I need to characterize this language:
$$
L = \{ s \in \Sigma^* \, | \, \{s\} \cdot A_1 \subseteq B_1 \land \ldots \land \{s\} \cdot A_n \subseteq B_n \}
$$
where $A_i, B_i$ are all regular languages. ...
- 133
5
votes
1
answer
111
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Logical Equivalents of Finite State Transducers
There's a notion of "regular" function on words in automata theory that corresponds nicely to functions in WS1S/Büchi Arithmetic/the logic of words with a prefix and equal-length relation. ...
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2
answers
266
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Defining regular language classes with disjoint union
Regular languages are typically defined using the operations of union, concatenation, and Kleene star. Likewise, there are restricted classes of regular languages defined via similar operations, for ...
- 8,896
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votes
1
answer
165
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Subset of regular languages
I have a system that is deciding a subset of regular languages and am curious if anyone has seen this type before and if it has a name I could use to research more.
Specifically consider the ...
- 292
11
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1
answer
165
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Check whether DFA accepts majority of words less than a cutoff with another DFA
Question
Let $M$ be some DFA that reads integers in base $k$. Does there always exist some other DFA $M'$ that also reads integers in base $k$, where $M'(x)$ accepts if and only if $M$ accepts the ...
- 1,204
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55
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Reference for cost of translating between regular language formalisms
It is well-known that regular languages can be defined equivalently via many formalisms, among which regular expressions, NFAs, finite monoids, Monadic Second-Order logic (MSO).
The cost (say in size ...
- 8,598
11
votes
1
answer
286
views
Existence of injective length-preserving rational function to a smaller alphabet
(This is a simpler rephrasing of an earlier question I have since deleted.)
Definitions
For this question, a finite-state transducer is like a standard NFA, except at each transition, the transducer ...
- 1,204
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votes
0
answers
45
views
Capturing a particular regular language with $O(m)$ states
In dx.doi.org/10.1006/inco.2001.3069 the authors defined $NID_m = \{ u\in \{0,1\}^* | \exists i : u_i \neq u_{i + m} \}$ and claimed it could be recognized by a NFA of size $O(m)$. The paper mentions ...
6
votes
1
answer
203
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star height of star-free languages
I'm interested in the (restricted) star-height of star free-languages.
Recalling the definitions:
the star height $h(\mathtt{e})$ of a regular expression $\mathtt{e}$ is
$0$ if $\mathtt{e}= \...
- 193
5
votes
1
answer
176
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Regular Expressions that converts into unambiguous automata
Brüggemann-Klein and Wood (1992) proved that a certain kind of regular expressions, that they call “Deterministic Regular expressions”, when converted into automata using the Glushkov's Construction, ...
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2
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219
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Reference request: An algebraic characterisation of LTL[XF]-definable word languages
I'm looking for a reference to the fact that LTL[XF]-definable languages (LTL where only the (strict) finally/future modality is allowed) correspond to the variety $\mathbf{R}$ (see: 1).
A similar ...
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votes
1
answer
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Is the function $f(a_1 \dotsm a_n) = a_1(a_1a_2)(a_1a_2a_3)\ \dotsm\ (a_1 \dotsm a_n)$ regularity-preserving?
A function $f: A^* \to A^*$ is regularity-preserving if, for each regular language $L$ of $A^*$, the language $f^{-1}(L)$ is regular. I think I have a proof, as a consequence of more general results, ...
- 4,771
2
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0
answers
100
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Necessary and sufficient condition for an infinite tree to be context-free
A Buchi automaton is non-empty iff it accepts an infinite word of the form $uv^\omega$ (here $u,v$ are finite words). In other words, if $\{w\}$ is an $\omega$-regular language, then it is of that ...
- 193
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1
answer
243
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DFSA and NFSA intersection problem
Given $k$ deterministic FSAs of $n$ states the intersection of their languages is empty is decidable in $n^{o(k)}$ time is an open problem.
For unbounded $k$ it is known the problem is $PSPACE$ ...
- 12.8k
2
votes
1
answer
167
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NP-Completeness of Finding Minimum Automaton, in Gold's paper
I have been investigating "learning automatas", and I came across reference to Gold's papers several times: "Complexity Of Automaton Identification From Given Data", and "...
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1
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428
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What is the time complexity of computing intersection and union of Nondeterministic Finite Automata (NFAs)?
Assume that $\mathcal{A} = (Q_A, \Sigma, \Delta_A, q_{i_A}, F_A)$ and $\mathcal{B} = (Q_B, \Sigma, \Delta_B, q_{i_B}, F_B)$ are two NFAs. What is the worst-case time complexity of computing $\mathcal{...
- 157
5
votes
1
answer
102
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Nonterminal descriptional complexity of regular languages
Recently I became interested in grammar complexity of regular language. Prior to searching for literature, I tried to investigate it on my own, proving two lemmas from comment below.
I am aware of an ...
- 411
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answers
194
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Regular languages accepted by an automaton with at most one transition per letter
I'm interested in the (very restricted) subset of regular languages for which there is an automaton having the following property: for every letter $a$ of the alphabet, the automaton has at most one ...
- 8,896
2
votes
1
answer
172
views
What graphs on $\mathbb{N}$ can be encoded as regular languages?
Suppose I represent the natural number 0 by "x", and use the symbol "s" for successor so that I get the following encoding of $\alpha : \mathbb{N} \rightarrow V$ of natural numbers ...
1
vote
0
answers
30
views
Decidability of regular partition construction given its existence
Let $G = (N,T,P,S)$ be a context-free grammar where $T,N$ are sets of terminals and nonterminals respectively, $P$ contains all the productions of the grammar, and $S \in N$.
If we know that $G$ is LL(...
- 111
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answers
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Bounds on the construction of regular expressions' intersection operator
There are references on the exponential worst-case of the intersection operator for regular expressions (see [1]). However, I was wondering if there are similar results for the construction process ...
user59861
13
votes
1
answer
378
views
Planarity of planar finite automata intersection
It was shown that any regular language can be specified by planar $\varepsilon$-free nondeterministic finite automaton (Bezáková, Ivona, and Martin Pál. "Planar finite automata."). Is it ...
- 421
3
votes
1
answer
139
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Rewrite relations - proof of correctness
Let $T \subseteq \Sigma^* \times \Sigma^*$ be a regular relation. We define the obligatory rewrite relation over $T$ as follows:
$$
R^{obl}(T) := N(T) \cdot (T \cdot N(T))^*
$$
$$
N(T) := Id(\Sigma^* ...
7
votes
1
answer
370
views
Kleene Algebra for star-free regular expressions
TLDR: Is there a notion of Kleene Algebra for star-free regular expressions?
Kleene Algebras are algebraic structures that are equivalent to regular expressions. A Kleene Algebra is an idempotent ...
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6
votes
2
answers
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2DFA to 1DFA - Converting two way deterministic finite automata to one way deterministic finite automata
How can I convert a 2DFA to a normal DFA. Is there an algorithm/elegant way to do that ?
I've been researching this for a few days but I coundn't find anything. Actually I want to implement that in ...
- 73
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votes
1
answer
746
views
What class of languages is recognized by finite-state automata with $k$ heads?
A DFA or NFA reads through an input string with a single head, moving left-to-right. It seems natural to wonder about finite-state machines that have multiple heads, each of which moves through the ...
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votes
1
answer
226
views
Complexity of DFA intersection in this specific case?
In general, the size of the DFA that recognizes the intersection of $n$ languages is exponential in $n$. However, in my case I am computing the intersection of a very restricted subset of possible ...
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votes
1
answer
180
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Arranging letters to make a word in a regular language
Fix a regular language $L$ on the alphabet $\{a, b\}$, and consider the following problem. I am given as input:
some number $m \in \mathbb{N}$ of copies of the letter $a$, and
some number $n \in \...
- 8,896
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votes
1
answer
140
views
Why are all finite languages regular? [closed]
It is said that "All finite languages are regular".
But the Pumping Lemma says that,
if a language is regular
one can find a 'large-enough' word w such that it can be decomposed into w = xyz such ...
2
votes
1
answer
495
views
Oncina-Garcia RPNI algorithm for learning DFAs
The question refers to this paper:
ftp://altea.dlsi.ua.es/people/oncina/articulos/asspr1992.pdf
Given a sample of $p$ positive and $n$ negative strings, RPNI constructs a consistent DFA in time $O((p+...
- 10.3k
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votes
0
answers
102
views
Does ${\bf CFLPAD}={\bf PPAD}$?
What happens if we define ${\bf PPAD}$ such that instead of a polytime Turing-machine/polysize circuit, a (non-)deterministic finite/push-down automaton encodes the problem?
I asked a similar ...
- 13.9k
1
vote
0
answers
48
views
Question About Turing Machine Computability [closed]
If p is a Turing machine then L(p) = {x | p(x) = yes}.
Let A = {p | p is a Turing machine and L(p) is a finite set}.
Is A computable? Justify your answer.
So I'm trying to figure out how to solve ...
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14
votes
2
answers
727
views
Automata learning without counterexamples
In Angluin's automata learning framework, a student aims to learn a regular language $L\subseteq \Sigma^*$ by asking two types of questions to his teacher:
Word queries: given $w\in \Sigma^*$, is $w\...
- 219
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votes
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284
views
Shortest string in the intersection of regular languages
Inspired by https://codegolf.stackexchange.com/questions/53310/shortest-universal-maze-exit-string
Each of the 138,172 valid mazes can be represented as a DFA with 9 states (including starting and ...
0
votes
1
answer
791
views
What is the practical importance of making or using a Turing complete language? [closed]
I get what a Turing machine is and what language is a Turing-complete language but when someone introduces me to a new programming language (like Solidity) and says it is Turing complete, what am I ...
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vote
0
answers
65
views
Rational power series over $\mathbb N \cup \{\infty\}$, rationality of singular part
Let $\Sigma$ be a finite alphabet, and consider the formel power series over $\Sigma$ considered as non-commuting variables with coefficients in the semiring $\mathcal N := \mathbb N \cup \{\infty\}$ ...
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3
votes
3
answers
162
views
Example of monoid $M$ such that $\operatorname{RAT}(M) \not\subseteq \operatorname{REC}(M)$
Let $M$ be a monoid, the family of rational sets $\operatorname{RAT}(M)$ is defined as the smallest set containing the finite subsets, and closed under union, concatentaion and the star operation. The ...
- 2,037
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votes
1
answer
244
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Generalisation of the statement that a monoid recognizes language iff syntactic monoid divides monoid
Let $A$ be a finite alphabet. For a given language $L \subseteq A^{\ast}$ the syntactic monoid $M(L)$ is a well-known notion in formal language theory. Furthermore, a monoid $M$ recognizes a language $...
- 2,037
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votes
1
answer
193
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Prove that L* is a regular language [closed]
Suppose that L is any language , not necessarily regular, whose alphabet is {0}; that is the strings of L consist of 0's only. Prove that L* is regular.
- 1
2
votes
1
answer
239
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Existence of an algorithm
I need to show that there exists a polynomial time algorithm that inputs a deterministic automata $A$, and decides if $A$ accepts a word w if and only if it also accepts any word obtained by permuting ...
- 21
7
votes
1
answer
253
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Finding a minimal DFA whose language has a desired intersection with another
Suppose I have regular languages $B \subseteq A$, with corresponding (known) minimal deterministic finite automata $M_A, M_B$.
I would like to find another regular language $C$ such that $B = A \cap ...
- 434
23
votes
2
answers
551
views
Testing whether letters can be scheduled to achieve a word in a regular language
I fix a regular language $L$ on an alphabet $\Sigma$, and I consider the following problem that I call letter scheduling for $L$. Informally, the input gives me $n$ letters and an interval for each ...
- 8,896
12
votes
1
answer
719
views
Parameterized complexity of inclusion of regular languages
I am interested in the classic problem REGULAR LANGUAGE INCLUSION. Given a regular expression $E$, we denote by $L(E)$ the regular language associated to it. (Regular expressions are on a fixed ...
- 2,143
-3
votes
1
answer
70
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Is there a non regular and regular language where the non regular is not a subset of the regular and the union is regular? [closed]
Does there exist languages $L1$, $L2$ where $L1$ is non regular, $L2$ is regular $L1\not\subset L2$ and $L1 \cup L2$ is regular?
- 103